22
BIOLOGIC BASIS OF SEX
by frequent gynandromorphs, XO males,
and dominant lethals among the rod and
ring zygotes. It has been suggested that the
instability is due to heterochromatic elements. Hinton (1959) has observed the
chromosome behavior of these types in
Feulgen mounts of whole eggs that were in
cleavages 3 to 8. He found strikingly abnormal chromosome behavior in these
cleaving nuclei. For some cell divisions
chromosome reproduction was interpreted
as being through chromatid-type breakage
fusion bridge cycles. As a result of this behavior mosaics are formed which are intermediate between those of the half gynandromorphs and those which occur much
later because of somatic crossing over. In
terms of volume of cells included, the abnormal types may include only a few cells
of the total organism, a fair proportion of
the cells, or a full half of the whole body.
These unstable ring chromosome mosaics
may be a part of the secondary reproductive system or for that matter any other
region of the body. When the mosaic cells
are incorporated in the region of sex organ
differentiation male or female type organs
or parts of organs may develop as governed
by the cell nuclei being X, XX or some fraction thereof.
Gynandromor|)lis appear sporadically and
rarely in many species but in some instances genes which activate mechanisms
for their formation are known. In the presence of recessive homozygous claret in the
eggs of D. siniulans, gynandromorphs constitute a noticeable percentage of the
emerging adults. The gene nearly always
operates on the X received from the mother
causing it to be eliminated from the cell.
The resulting gynandromorphs are similar
to those of D. melanogaster. The fact that
the claret gene should affect the X and a
particular X chromosome is suggestive of
the manner in which given chromosomes arc
eliminated in Sciara. Other types of sex
mosaics will be found in the descriptions of
other species, i)articularly in the Hymenoptci'a.
C. PARTHENO(iENESIS IN DROSOPHILA
Parthenogenesis is of interest as it
changes the sex ratios in families and brings
to light new sex types and novel methods
for their development (Stalker, 1954), A
survey of 28 species of Drosophila showed a
low rate of parthenogenesis in 23 species.
Adult progeny were obtained for only 3
species. For D. 'parthenogenetica the original rate was 8 in 10,000 whereas that for D.
polymorpha was 1 in 19,000. These rates
could be increased by selection of higher
rate parents: 151 and 70 per 10,000 unfertilized eggs of the first and second species
respectively.
D. parthenogenetica diploid virgins produced diploid and triploid daughters as well
as rare XO sterile diploid males. Triploid
virgins produced diploid and triploid females and large numbers, 40 per cent, of
sterile XO diploid males. Diploid virgins
heterozygous for sex-linked recessive garnet
produced homozygous and heterozygous
diploid females as well as +/+/g and
+ /'g/g triploid females. No homozygous
wild-type or homozygous garnet triploid females or garnet mosaics were found. Diploid females crossed to fertile diploid males
produced few if any polyploid progeny or
jjrimary X chromosome exceptional types.
Of the unfertilized eggs from diploid virgins
which started development, 80 per cent died
in late embryonic or early larval stages.
The i)arthenogenesis in diploid females depended on two normal meiotic divisions followed by fusion of two of the derived haploid nuclei to form diploid progeny, or the
fusion of three such nuclei to form triploitl
progeny. In the triploid virgins similar fusions of the maturation nuclei may produce
diploid and triploid females but the large
number of dii)loid XO sterile males were
picsunicd to be the result of cleavage without prior nuclear fusion. Such cleavages
without fusion in eggs of dijiloid virgins
would lead to the production of haploid
embryos. They were presumed i-esponsible
for the large early larval and embryonic
<h'atlis. These obser\ali()ns have been confirmed by the study of S|)rackling (1960)
in\-olving some 2200 eggs at various stages
of cleavage. Evidence from XXY diploid
virgins indicated that biiuiclcar fusion in
unfertilized eggs involved two terminal
haploid nuclei or two central nuclei. The
fact that tetraploids were not observed as
progeny of ti'iploid vii'gins was considered
indicative of relative inviability of this
FOUNDATIONS FOR SEX
23
type. Successful parthenogenesis was under
partial control of the inheritance as 80 generations of selection increased the rate
about 20-fold. Similarly outcrossing to bisexually reproducing males and reselection
resulted in both pronounced increases in
and survival of the parthenogenetic types.
Carson, Wheeler and Heed (1957) and
Murdy and Carson (1959) have established
a strain of Drosophila mangabeirai with
only thelytokous reproduction. Males have
been captured in nature but are rare. Fecundity of the virgin females is low but the
egg hatch is 60 per cent and 80 per cent
survive to adult stage. The progeny of the
virgins are always diploid. In meiotic spindle formation D. mangabeirai differs from
other Drosophila species in that its orientation increases the probability for fusion of
two haploid nuclei into structurally heterozygous diploid females. The study of
Feulgen whole mounts of freshly laid eggs
indicated automictic behavior with two
meiotic divisions followed by a fusion of
two of the four haploid meiotic products.
The absence of adult structural homozygotes in wild populations is probabl}^ explained by death during early development
and by possible fusion of second division
meiotic products derived from different secondary oocytes. Stalker (1956a) postulated
such selective fusion in order to account for
the heterozygous condition in females of
Lonchoptera dubia, an automictic, parthenogenetic fly in which males are rare or unknown.
A case in which jihenotypically rudimentary females, supposed homozygous for r/r
give rare and unexpected type progeny, has
suggested that polar body fusion may also
take place in D. melanogaster (Goldschmiclt, 1957). The rudimentary mothers
producing the peculiar type are interpreted
as formed by a most unusual series of
events: a fertilization nucleus derived from
the fusion of an r containing egg fertilized
by an r containing sperm and a polar copulation nucleus derived from the fusion of a
polar body containing an r genome and one
having wild type. Both cell types become
incorporated into the ovary. The progeny
which come from these supposed rudimentary mothers are presumed to be derived
from the maturation into eggs of the cells
derived from the heterozygous i)olar copulation nuclei. If these progeny-producing
rudimentary mothers arise in the presumed
manner they give the basis for a parthenogenetic mode of reproduction and the sex
types which have been described in other
Drosophila species by Stalker and Carson.
There are similar, as well as other forms
of parthenogenesis which affect sex (Smith,
1955) or assist in maintaining trijiloid conditions (Smith-White, 1955). A number of
these types have been reviewed by Suomalainen (1950, 1954). The reader may be referred to this material for other cases and
chromosome behaviors.
D. SEX INFLUENCE OF THE Y CHROMOSOME
The first function discovered for the Y
chromosome in D. melanogaster was that it
was necessary to male fertility (Bridges,
1916). Two and possibly more Y chromosome-borne, genetic factors were involved
(Stern, 1929). Gamete maturation when
these factors were lacking ceased just short
of the sperm's becoming motile (Shen,
1932). The motility conferred on the sperm
by the presence of the Y chromosome factors was fixed for the testes at an early
stage of development as transplantation experiments, sterile testes to fertile larvae
and fertile testes to sterile larvae, showed
motility to be a property determined by
early localized somatic influences on the
developing gametes or predetermined in the
diploid phase (Stern and Hadorn, 1938).
This Y chromosome function was sex limited, because females without a Y were the
normal fertile females and those with an
extra Y also were fertile.
Neuhaus (1939) followed by Cooper
(1952, 1959) and Brosseau (1960) further
analyzed the Y chromosome for fertility
loci. The latter showed at least two fertility
loci on the short arm and five on the long
arm of the Y chromosome. Data are compatible with a linear order of the genes. An
additional fertility factor common to the X
and Y was suggested. The Y chromosome
fertility factors consequently fall in line
with Bridges' concept of multiple gene loci
distributed in a more or less random manner which may affect sex.
The Y chromosome has other attributes
which help to explain its significance to sec
24
BIOLOGIC BASIS OF SEX
ondary if not primary sex characteristics.
As with many other species it has loci for
genes which are also found in the X chromosome, i.e., bobbed, as well as a limited
number of bands in the salivary gland chromosome. Nucleolus organizers and at least
two specialized pairing organelles similar
to those in the X chromosome are found
within the Y chromosome (Cooper, 1952,
1959). One of the most significant properties is the effect of extra Y chromosomes on
the variegation observed for various gene
phenotypes either in the normal chromosome pattern or in that accompanying
translocation. In variegation one Y chromosome as extra to the normal complex is
sufficient to eliminate or more rarely to
much reduce the variegated expression
(Gowen and Gay, 1933). When the Y chromosomes are 2 above the normal complement, the phenotypes gain two new features
(Cooper, 1956). Both males and females
become variegated in the expression of their
eye characteristics. The males become sterile. These effects are unexpected for they
are counter to any previous trends in the Y
effects on these characteristics. They have
reversed the direction of the effects as established by the two previous chromosome
types. The variegation of the XX2Y + 2A
females and X3Y + 2A males resembles
that of the XX + 2A females and XY +
2A males but is more extreme, whereas the
XXY + 2A and X2Y + 2A are largely
nonvariegated. The fertility relations are
equally aberrant: the X3Y + 2A males
have the same type sterility through loss of
sperm motility as that of the XO + 2A
males. Bundles of sperm are formed but
they do not become motile. Full-sized Y
chromosomes are not required to bring
about these effects, because females having
a whole Y plus a piece of a second, or males
with 2Y plus a piece of a third, will show
the effects.
The fractional Y chromosomes furnish
opportunities to test for the partial independence of the variegation and sterility effects. The two Y hyperploid males differ in
their degree of fertility according to the
fraction of the Y chromosome which may
be present whereas the effects on variegation may be constant among groups. This is
in accord with the sterility l)eing in part
independent of the factors causing the variegations. Similarly, the variegations may
be shown to be partially free of the action
of some elements that are not themselves
members of the two sets of factors influencing fertility in the normal male.
Other phenotypic irregularities appear;
eye facets may be roughened, legs shortened, and wing membranes become abnormal. On the negative side two extra Y chromosomes in females homozygous for the
transformer gene, tra, do not increase in
maleness or function.
The variegations of the so-called V-type
position effects with translocations are suppressed, as in the normal type described,
by one extra Y but are nonetheless variegated when two extra Y chromosomes are
present. That these effects are caused by
there being two supernumerary Y's is indicated by the fact that XX2Y females are
fertile and X3Y males sometimes lose a Y
chromosome in their germinal tracts and
become fertile. A number of mechanisms
have been suggested to account for these
results but most have proven unsatisfactory. A balance interpretation for the X, Y
and autosomes like that for sex, as suggested by Cooper (1956) is compatible with
the somatic cell variegations for euchromatic loci transferred to the heterochromatic regions and the sterility-fertility
relations expressed by the different chromosomal types.
The variegation effects of the Y chromosome take on further significance. Baker
and Spofford (1959) have shown that 15
different fragments of the Y chromosome
when studied for their contributions to variegation differ in their effects with the differences often not related to the size of the
fragment, thus indicating that the Y chromosome has linearly differentiated factors
capable of modifying the variegated phenotype.
Other indications of genetic activity of
the Y chromosome were given by Aronson
(1959) in her study of the segregation observed in 3rd chromosome translocations. A
deficiency for the region of the 3rd chromosome centromere is lethal when homozygous. Both males and females are fully
\'iable when this deficiency is heterozygous.
XO or haplo IV deficient males die. How
FOUNDATIONS FOR SEX
25
ever, in the presence of a Y chromosome the
deficient haplo IV males become viable.
The lability of this last class indicates that
the Y chromosome is genetically active, can
compensate for the autosomal deficiency,
and thus alter the progeny sex ratio.
In D. virilis the situation is somewhat
different from that observed by Cooper in
1956 in D. melanogaster. Baker (1956) has
shown that, in a translocation, males having
two Y chromosomes plus a Y marked with
a 5th chromosome peach are fertile. These
results seem to indicate a species difference
in the effect of the extra Y on fertility or
the Y with the inserted peach locus is not
a complete Y and in consequence the true
composition of these males is X + 2Y plus
a fragment of the Y. The X chromosomal
associations in the multichromosomal types
are shown to be by trivalents or by tetravalents. The segregation data indicate that
the pattern of disjunction of trivalents is a
function of the particular Y chromosome
involved. In X2Y males with normal Y's or
with one normal and one marked Y, the Y's
disjoin almost twice as frequently as they
do from trivalents with two identical Y's.
Tetravalent segregation is almost entirely
two by two, with no preference for any of
the three types of disjunction.
An odd situation was reported by Tokunaga (1958) in substrains of Aphiochaeta
.vanthina Speiser. When a male of the substrain was crossed to individuals bearing
3rd chromosome genes of the original
strains, the mutant genes for brown, and so
on, behaved as if they were partially sexlinked in the following generations. On the
other hand, when a female carrying the partially sex-linked genes on the X and Y
chromosomes. Abrupt or Occhi chiari, was
crossed to the male of the substrain the
characters segregated as though they were
autosomal. As a working hypothesis it was
suggested that in this species the Y chromosome had the major male determining
factors. The "special" male arose as a translocation of these factors to the third chromosome with the consequent change in linkage
relations. Data on the role of the X chromosome in sex determination in this species
have not yet been obtained but if they support the interpretation they indicate real
differences between this species and that of
Drosopliila in the location of the sex genes.
The results are reminiscent of those obtained by Winge in Lebistes as well as those
in Melandrium and other forms in which
the Y or W chromosomes may contain
strong sex genes for either sex. They would
further support the thesis that sex genes
may be distributed to almost any loci within
the inheritance complex.
E. M.\TERNAL INFLUENCES ON SEX RATIO
Aside from chance and specific genetic
factors, sex ratio is subject to effects from
agents intrinsic in the cells of the mothers
(Buzzati-Traverso, 1941; Magni, 1952).
Strains of Drosophila bifasciata (Magni,
1952, 1953, 1957), D. prosaltans (Cavalcanti and Falcao, 1954), D. willistoni and
D. paulistorum Spassky, 1956 have been
isolated which were nearly all of the female
sex even though the mothers were outbred
to other strains having normal ratio bisexual
progeny. Study of these strains by the above
workers and Malogolowkin (1958) IVIalogolowkin and Poulson (1957), and Malogolowkin, Poulson and Wright (1959), as
well as by Carson (1956) have shown inheritance strictly through the mother regardless of the genetic nature of the males
to which they were bred. The unbalanced
ratio was retained even when the original
chromosomes had been replaced by homologous genomes from lines giving normal male
and female progenies. Transmission of this
unbalanced sex ratio was through the cytoplasm. Eggs fertilized by Y-bearing sperm
died early in the course of development.
Malogolowkin, Poulson and Wright (19591
have shown that the high female ratio and
embryonic male deaths may be transferred
from affected females to those which do not
normally show the condition through injection of ooplasm from infected females.
Ooplasm of this same type is, w^hen injected
into males, suflficient to cause death to occur within 3 days. In the females a latent
period of 10 to 14 days after ooplasm injection was apparently necessary to establish
egg sensitization. Once established the condition could be transmitted through the
female line for several generations. The
ooplasm injections were not as efficient in
establishing these lines as females found
naturally infected. Unisexual broods may
26
BIOLOGIC BASIS OF SEX
fail to appear, in some instances fail to
transmit the condition or produce intermediate progeny ratios, as well as in some
instances to skip a generation. The infectious agent was found to vary in different
species. Magni (1953, 1954) for D. bifasciata found that temperature above normal tended to remove the cytoplasmic agent
making it ineffective. This result has a parallel to the action of temperature on certain
viruses, as for instance that involved in one
of the peach tree diseases. On the other
hand, Malogolowkin (1958) ior D . willistoni
found no temperature effect. Malogolowkin
further found that the cytoplasmic factor
was not independent of chromosomal genes
since some wildtype mutant strains induced
reversions to normal sex ratio. Recently
Poulson has established the complete correlation of the high female progeny characteristic with the presence of a Trepomena in
the fly's lymph. As with mouse typhoid variations, lethality was genotype dependent.
These cases have interest from more than
the sex ratio viewpoint. Cytoplasmically
inherited susceptibility of some strains of
D. 7nelanogaster to poisoning by carbon dioxide as studied by L'Heritier (1951, 1955)
depended on the presence of some cytoplasmic entity which passed through the egg
cytoplasm and also, but less efficiently, by
means of the male sex cells to the progeny.
The carbon dioxide susceptibility was transmitted through injections of hemolymph or
transplantation of organs of susceptible
strains. The transmissible substance had a
further property of heat susceptibility. The
COo susceptibility differed from that of "sex
ratio" in being partially male transmitted.
It agrees with sex ratio" D. bifasciata in
being heat susceptible but differs from D.
willistoni "sex ratio" in this respect.
D. bifasciata may behave differently than
D. willistoni in that Rasmussen (1957) and
Moriwaki and Kitagawa (1957) both conducted transplantation experiments with
negative results. However, it is jiossible that
these experiments may be affected by a
different incubation period for the injected
material as contrasted with that for D.
willistoni. A range of possibilities evidently
exist for extrinsic effects in sex ratio.
Carson (1956) found a female producing
strain of D. borealis Patterson, which car
ried on for a period of 8 generations, produced 1327 females with no males. The
strain showed no chromosomal abnormalities. It had 3 inversions. The females would
not produce young unless mated to males
from other strains having biparental inheritance. This requirement, together with
gene evidence, showing that the females
were of biparental origin, is against the female progenies being derived by thelytokous
reproduction.
F. MALE-INFLUENCED TYPE OF
FEMALE SEX RATIO
Sturtevant in 1925 described exj^eriments
with a stock of D. affinis in which a great
deficiency of sons was obtained from certain
males, regardless of the source of females
to which such males were mated. The few
males obtained from such matings were normal in behavior but some of the sons of
females from such anomalous cultures again
gave very few sons (]Morgan, Bridges and
Sturtevant, 1925).
Gershenson (1928) in a sampling of 19
females caught in nature found two that
were heterozygous for a factor causing
strong deviations toward females (96 per
cent to 4 per cent males) whereas the normal D. pseudoobscura ratio was nearly 1 to
1. The factor was localized in the X chromosome and was transmitted like an ordinary
sex-linked gene. Its effect was sex limited
as it was not manifest in either heterozygous or homozygous females. It had no
effect on the development of zygotes already formed but strongly influenced the
mechanism of sex determination through the
almost total removal of the spermatozoa
with the Y chromosome from the fertilization process. Egg counts showed the divergent ratio toward females was not caused
by death of the male zygotes inasmuch as
there was no greater mortality from such
cultures than from controls giving 1 to 1 sex
ratios.
Sturtevant and Dobzhansky (1936)
showed that an identical or nearly identical
phenotypc to that obscM'ved in Drosophila
obscura was present in D. pseudoobscura.
The D. pseudoobscura carrying the factor
were scattered over rather wide geographical areas. Comparable types also were found
in two other species D. athabasca and D.
FOUNDATIONS FOR SEX
27
azteca. This genie "sex ratio"' sr lies in the
right limb of the X of races A and B of
D. pseudoobscura. Like the other cases
analyzed, males carrying sr have mostly
daughters and few sons regardless of the
genotypes of their mates. Structurally the
female sex ratio came through modification
of the development of the sex cells of the
male to give a majority of X-bearing sperm.
Cytologic study showed that in "sex ratio"
males the X underwent equational division
at each meiotic division, whereas the autosomes behaved normally. The Y chromosome lagged on the first spindle, remained
much condensed, and its spindle attachment
end was not attenuated. The Y chromosome
was not included in either telophase group
of the first meiotic division but was left behind. It was sometimes noted in one of the
daughter cells where it formed a small nucleus. Among 64 spermatocytes examined,
all had an X chromosome and none a Y
chromosome in their main nuclei. The micronuclei containing Y played no further
part in the division, became smaller and
exceedingly contracted. The final fate of the
micronuclci was uncertain, but there was no
indication that any spermatids died or were
abnormal.
G. HIGH MALE SEX RATIO OF GENETIC ORIGIN
In 1920, Thompson described a recessive
mutant in D. melanogaster which killed all
homozygous females but changed the male
phenotypes only slightly, the wings standing erect above the back. The locus of the
mutant was 38 in the X chromosome. This
mutant was a leader for a class in which the
genes affect only one sex but are innocuous
to the other.
Bobbed-lethal, a sex-linked gene found
i)y Bridges, is a gene of this class but one in
which the mechanism of protection to the
other sex is known. It kills homozygous females but does not kill the males because of
the wild type allele which the males have in
their Y chromosomes. The presence of this
bobbed-lethal in a population consequently
leads to male ratios higher than wild type.
A recessive gene in chromosome II, discovered by Redfield (1926), caused the
early death of the majority of female zygotes and led to a sex ratio of about 1 female to 5.5 males. The effect was trans
mitted througli both males and females. The
missing females may have died largely in
the egg stage although disproportionate
losses also occurred in the larvae and pupae.
The maternal effect was attributed to an
influence exerted by the chromosome constitution of the mother on the eggs before
they left the mother's body. Because of this
maternal lethal, the families from these
mothers have the normal number of sons
but few or no daughters.
A culture was observed by Gowen and
Nelson (1942) which yielded only male
progeny, 136 in all. Some of the male progeny were able to transmit the male-producing characteristics to half of their daughters
without regard to the characteristics of the
mates to which they were bred. The inheritance was without phenotypic effect on
the males. When present in the heterozygous condition in females, the female's
own phenotype gave no indication of the
gene's presence. The inheritance was sex
limited in that it affected only the eggs laid
by the mothers carrying it. In these eggs it
acted as a dominant lethal for the XX zygotes. The gene was found located in the 3rd
chromosome between the marker genes for
hairy and for Dicheate at approximately 31.
The X eggs carrying the gene, Ne, died in the
egg stage at between 10 and 15 hours under
25°C. temperature. The gene was as effective in triploids as in diploids. One dose
of this gene in triploids caused them to have
only male progeny and male type intersexes.
The presence of this gene caused the elimination of any embryos with chromosomal
capacities for initiating and developing the
primary or secondary female sexual systems. Since the gene itself was heterozygous
in the female the meiotic divisions of the
eggs would cause the gene to pass into the
polar bodies as often as to remain in the
fertilization nucleus yet the lethal effects
are found in all eggs. The antagonism was
between the egg cytoplasm and the XX
fusion products. Supernumerary sperm of
the Y type were not sufficient to overcome
the lethal effects. An XY fertilization nucleus was necessary for survival.
This case has parallel features with that
observed by Sturtevant (1956) for a 3rd
chromosome gene that destroys individuals
bearing the first chromosome recessive gene
28
BIOLOGIC BASIS OF SEX
for prune. The gene responsible was found
to be a dominant, prune killer, K-pn, which
was located in the end of the 3rd chromosome at 104.5. Prune killer was without
phenotypic effect so far as could be observed except that it acted as a killer for
flies containing any known allele of prune.
It was equally effective in either males or
females, hemizygous or homozygous, for
prune. The larvae died in the 2nd instar
but no gross abnormalities were detected
in the dying larvae. This case has interest
for the Ne gene in that the killer gene occupies a locus in the 3rd chromosome although removed by about 70 units from Ne,
and acts on a specific genotype, the prune
genotype, whereas Ne acts on the specific
XX genotype. The known base for action
of the prune killer is genetically much narrower than that for the female killer, Ne,
in that prune killer acts on an allele within
a specific locus in the X chromosome, and
Ne acts on a type coming as a product of
the action of two whole sex chromosomes. It
is, of course, conceivable that when ultimately traced each action may be dependent
upon specific changes of particular chemical syntheses. The action of these genes is
also of interest from another viewpoint.
In mice there is a phenotype caused by
the homozygous condition of a recessive
gene (Hollander and Gowen, 1959) which
acts on its own specific dominant allelic
type in its progeny so as to cause an increased number of deaths between birth
and two weeks of age, as well as causing the
long bones to break and the joints to show
large swellings. The lethal nature of this
interaction is not a product of the mother's
milk nor does it show humoral effects such
as those observed with erythroblastosis in
the human. The interallelic interaction is
sex limited in that it is confined to the
mother and is without effect when the male
has the same genotype.
H. FEMALE-MALE SEX RATIO INTERACTIONS
A case in D. affinis involving the interaction of a "female sex ratio" factor and an
autosomal "male sex ratio" factor has been
studied by Novitski (1947). Starting from
stock which had a genetic constitution for
the "sex ratio" X chromosome which ordinarily causes males carrying it to produce
only daughters, he was able to establish a
recessive gene in chromosome B in whose
presence only male offspring resulted. The
genetic constitution of the male was alone
important. High sterility accompanied the
"male sex ratio" males breeding performance. The "male sex ratio" parents yielded
95 fertile cultures having an average of 25
individuals per culture. Females appeared
in 10 of these cultures with an average of 3
per culture for those producing females. The
total sex ratio was 77 males per female. The
males were morphologically normal. They
carried an X chromosome of their mothers.
Cytologic observation of spermatogonial
metaphases of 3 progeny showed that the
Fi males may or may not have carried a Y
of their fathers. This agreed with the tendency for sterility in these "male sex ratio"
males. The ventral receptacles of the females from 4 such sterile cultures when examined proved devoid of sperm. The occasional female offspring of the "male sex
ratio" males had one X chromosome from
each parent. Females mated to "male sex
ratio" males show large numbers of sperm
in the ventral receptacles (7 out of 8 cases) ,
although such females had usually produced
no or very few offspring. The sperm, if
capable of fertilization, must have had a
lethal effect on the zygotes. The recessive
nature of the factor in chromosome B indicated that its potential lethal effect originated during spermatogenesis rather than
at the time of fertilization. This lethal period corresponds to that when the "female
sex ratio" factor in the X chromosome is
active.
The research on sex ratio in Drosophila
reviewed shows that through the interplay
of the sex chromosome-located and autosomal-located factors all types of sex ratios
from only females in the family to only
males in the family may be generated.
V. Sex Determination in Other Insects
Sciara, a fungus gnat, offers sex-determining mechanisms quite different from any
yet offered in Drosophila. Sciara is unique,
yet in its uniqueness, it illustrates basic
facts that were rediscovered in other species only through the study of abnormal
FOUNDATIONS FOR SEX
29
forms some of which were created as induced developmental, chromosomal, or hormonal abnormalities. The complexities responsible for the remarkable facts were
analyzed by Metz and his collaborators.
The following brief review is based upon
Metz's (1938) summarization of the chromosome behavior problem to which the
reader is referred for further information.
Of Sciara species studied 12 out of 14 have
their basic chromosome groups composed of
three types of chromosomes: autosomes,
sex chromosomes, and "limited" chromosomes. Two species, S. ocellaris Comstock
and S. reynoldsi Metz, lack the "limited"
chromosomes. Two sets of autosomes and
three sex chromosomes are found in the
zygotes of all Sciara species at the completion of fertilization. The behavior of these
chromosomal types will be considered in
sequence.
The autosomes behave normally in somatic mitosis and in oogenesis. There is
cytologic and genetic evidence for synapsis,
crossing over, random segregation, and regular distribution of chromosomes and genes
in the female.
In spermatogenesis the story is quite different. The first maturation division is unipolar. Genetic evidence shows a complete,
selective segregation of the maternally derived autosomes and sex chromosomes from
those of paternal origin. The paternal homologues move away from the pole, are
extruded, and degenerate. The second
spermatocyte division is likewise unequal
and one of the products, a bud, degenerates.
Thus a spermatogonial cell passing through
meiosis gives rise to only one sperm. At the
second spermatocyte division all of the
chromosomes (maternal homologues) except
the sex chromosome undergo an equational
division but both halves of the sex chromosome enter into the same nucleus. This nucleus becomes the sperm nucleus. The chromosomes at the opposite pole form a bud
and degenerate. Fertilization of the Sciara
egg is normally monospermic not polyspermic.
The sex chromosomes XXX of the fertilization nucleus are derived, two from the
sperm and one from the oocyte. Their destiny depends on whether the egg they are
in develops into a male or a female imago.
In male early development, those nuclei
which are to become male soma lose the two
sex chromosomes XX, contributed by the
father's sperm, to give X + 2A soma. These
chromosomes fail to complete mitosis at
the 7th or 8th cleavage division and are left
to degenerate in the general cytoplasm when
there are no true cells in the soma region
and no membranes surround the nuclei.
Those embryos which are to become female
soma at the same cleavage cycle eliminate
but one paternal X chromosome. On a chromosome basis the soma cells respectively
become X, plus two sets of autosomes, give
rise to males on differentiation, or become
XX + 2A and develop female organs (Du
Bois, 1932). The germ line nuclei for each
sex, on the other hand, remain unrestricted
in their development. They retain their
XXX constitutions until the first day of
larval life, or about 6 hours before the formation of the left and right gonads (Berry,
1941), when they eliminate a single paternally derived X. The X which is rejected or
makes its own exit is always one of two
sister chromosomes contributed by the
father. The process of loss is strikingly different from that noted in the soma-building
nuclei. Both cell walls and nuclear membranes are present. The path of the X chromosome is through the nuclear membrane
into the cytoplasm where degeneration
eventually takes place. The loss occurs at
a time when there is no mitotic activity and
the chromosomes are separated from the
cytoplasm by an intact nuclear membrane.
Some Sciara species are characterized by
females which produce only unisexual families — practically all females or practically
all males. Genetically, the sex of progeny is
accounted for by sex chromosomes, X' and
X, which are so designated because of their
physiologic properties. Mothers having only
female progeny are characterized by always
having the X' chromosome in all their cells,
X'X + 2A, whereas mothers whose progeny
are all males are XX + 2A (Moses and
Metz, 1928). The all female and all male
broods are observed in about equal numbers. The male has no influence on sex ratio.
Normally the progeny in all female broods
will be X'X + 2A or XX + 2A in soma
30
BIOLOGIC BASIS OF SEX
and germ lines, whereas the all male progeny broods will be only X + 2A in the soma
and XX + 2A in the germ line.
Studies of Grouse (1943, 1960a, b) show
nondisjunction may occur and eggs entirely
lacking sex chromosomes or having double
the normal number may be produced. When
the nondisjunctional eggs lacking X chromosomes are from X'X females and are fertilized by sperm contributing two sister X
chromosomes, one X (as expected of X'X
mothers, not two as expected of XX cells) is
eliminated at the 7th or 8th cleavage to give
cells which develop into "exceptional" males
with XO + 2A soma and XX + 2A germ
line, all X chromosomes being of paternal
origin. The casting out of the single X chromosome is consequently controlled by the
characteristics of the egg cytoplasm derived
from the X'X mother rather than by the
kind of chromosomes present in the nuclei
at the 7th or 8th cleavage stage of the eml)ryo.
Similarly when nondisjunctional eggs
having both XX chromosomes of the XX
mothers are fertilized by the normal spermbearing XX chromosomes, the zygotes are
XXXX. At the 7th or 8th cleavage both
paternal X chromosomes are eliminated and
the resulting soma develops into an exceptional" female, XX + 2A, often with 3 X's
in her germ line. These observations confirm the earlier interpretations that the X'X
or XX constitution of the mother conditions
her eggs respectively to cast out 1 or 2
parental X chromosomes at the 7th or 8th
cleavage according to the cytoplasmic constitution of the egg. Somatic sex development is visually determined only after this
stage when the chromosomes of the somatic
cells take on the familiar aspect of either
XX + 2A for the females or X + 2A for the
males.
Although at present there are few examples in other species, this cytoplasmic conditioning of early embryologic development
by the mother's genotyj)e may be a common
rather than a rare occurrence of development. The expression of the events to which
this control may lead may be quite different in different cases. The spiral of snail
shells was an early recognized case (Sturtcvant, 1923) . In Drosophila, a gene acting
through the mother's genome allows onlv
male embryos to survive (Gowen and Nelson, 1942), suggesting that this gene acts
through her cytoplasm in a manner comparable to that of the X' and X chromosomes of Sciara. In either case the genotype would not be considered a primary sex
factor, profound as the effect on sex may
ultimately be.
Sciara also has strains or species where
the progeny of single matings are of both
sexes, bisexual, yet the chromosomal elimination mechanisms remain as described
above save for the fact that they now operate within broods rather than between
broods. Sex ratios for the families within
these bisexual strains are extremely variable, 1:0 or 0:1 ratios not being infrequent
and 1 : 1 ratios being the exception. An instance of a bisexual strain arising from a
unisexual line has been analyzed by Reynolds (1938). The females were found to be
3X in their germ line and produced 2X eggs
which developed into daughters and X eggs
which became sons. Loss of the extra X
from this line resulted in the line's return to
unisexual reproduction.
In general, bisexuality as contrasted with
unisexuality seems to be caused by differences in the X'X-XX mechanisms, either
specific for the mechanism, or induced by
modifying genes which cause different embryos within the same progeny to cast out
sometimes one or sometimes two X chromosomes from all their somatic nuclei. This
casting out occurs uniformly for all nuclei
of a given embryo as is shown by the fact
that sex mosaics or gynandromorphs are as
seldom observed in bisexual as unisexual
strains.
Some species of Sciara have large chromosomes which are in essence "limited" to
the germ line since they are lost from the
somatic nuclei at the 5th or 6th cleavage
division. Other species lack these chromosomes, yet agree with the rest in the behavior of their remaining chromosomes and
in sex determination. So far as is now
known the "limited" chromosomes seem
empty of inheritance factors influencing either sex or unisexual vs. bisexual broods or
for that matter other characteristics (their
persistence seems to make this latter unlikely I. Their presence does lead to a question of the efficacv of desoxvribonucleic acid
FOUNDATIONS FOR SEX
31
(DNA) as the all inclusive agent in inheritance for they are clearly DNA-positive.
These cytogenetic observations clear up
most of the events leading to sex differentiation and the delayed time in embryologic
development when it takes place, but, as
INIetz points out, other puzzling questions
are raised. Observed chromosome extrusions
from cell nuclei are rarities today even
though discovered for Ascaris 60 years ago.
Why should this mechanism be so well defined in Sciara? Why should the mode of
elimination be so accurately timed and yet
be different in method and time for the
soma and germ cell lines? Two of the three
X chromosomes in the fertilized egg are
sisters from the father and should be identical. What is special in the 7th or 8th cleavage that causes elimination in the soma
plasm but not in the germ plasm? Why
should the casting out of one of these same
paternal X's in the germ plasm of both
sexes be reserved for a much later stage in
cleavage and by a different procedure?
The observations of Grouse (1943, 1960a),
obtained from translocations and species
crosses, are critical in showing that the
chromosome first moA'ing in its entirety to
the first differentiating pole of the second
spermatocyte division is the X and is the
one taking part in the later postfertilization
sex chromosome elimination of the 7th or
8th cleavage. The X heterochromatic end of
the chromosome and not the centromere region seems to be responsible for the unique
behavior of this chromosome (Grouse,
1960b). Induced nondisjunctional eggs of
X'X (female-producing) mothers having as
a consequence no sex chromosomes, when
fertilized by the normal sperm bringing in
XX chromosomes, develop into embryos
eliminating one of these X's at the 7th or
8th cleavage, as expected of the eggs of
X'X mothers, and become "exceptional"
males with X + 2A soma and XX paternal
germ line. Imagoes of these embryos become
functional but partially sterile males transmitting the paternal X, a reversal of the
normal condition. Similarly the nondisjunctional eggs retaining both X's, XX
from male-producing mothers, and having
4 X's on fertilization eliminate the two paternal X's, as occurs normally in XXX eml)ryos, to become "exceptional" females with
2X or sometimes in species hybrids 3X
soma.
Phenotypic sex in Sciara on this evidence
depends on the adjustment of the X chromosome numbers and their contained genes
with this adjustment regularly taking place,
not at fertilization as in most forms like
Drosophila, but at the 7th or 8th cell cleavage of embryologic development. The X' vs.
X chromosomes of the mother predispose
her haploid egg cytoplasm to time specific
chromosome elimination. The germ line cells
on the other hand may regularly have other
chromosome numbers than the soma or exceptionally tolerate other numbers as extra
X's (Grouse, 1943), or extra sets (Metz,
1959).
Triploids of 3X and 3A soma have not
been found in pure Sciara species. Salivary
gland cells of a triploid hybrid S. ocellaris x
aS. reynoldsi have two sets of S. ocellaris and
one of S. reynoldsi chromosomes (Metz,
1959). Ghromosome banding in 2X -I- 3A,
3X + 3A larval glands showed the »S. ocellaris homologues were heterozygous. The
3X + 3A type chromosomes were of typical
female appearance. The 2X:3A-type had
X chromosomes of typical male type, very
thick, pale and diffuse. The mosaic salivaries were a mixture of the two types of
cells. These results suggest that the 3X:3A
would be a typical female. The intersexes
2X -I- 3A conceivably have a range in male
and female organ development depending
on how the S. ocellaris and S. reynoldsi
chromosomes act. If the chromosomes are
equivalent, the gene expression would be
expected to be that of a 2X to 3A or a
phenotypic intersex. If they act separately
the S. ocellaris genes would be in balance for
female determination, whereas the S. reynoldsi autosomal genes would have no X S.
reynoldsi genes to balance them and presumably would be overwhelmingly male in
effect. The phenotypic outcome would be
in doubt.
The maternally governed cleavage and
chromosomal sequence occurring before the
8th embryonic cell division, although related to the subsequent events leading to the
particular sex, is unique to Sciara and its
relatives. Phenotypic sex expression apparently starts with the somatic nuclei having
either X + 2A or XX + 2A as their chro
32
BIOLOGIC BASIS OF SEX
mosomal constitutions. Sciara is like Drosophila and many other genera in its basic
sex-determining mechanism. There is a sexindifferent period when the maternal genotype may influence development through
cytoplasmic substances. This is followed by
active differentiation when the sex phenotypes may be influenced by various agencies
but when passed becomes fixed for phenotypic sex. The indifferent period may represent a fairly large number of early cell generations as in amphibia or fish. Somatic
and germ cells are labile but are normally
susceptible to control only by forces developed within the organism as present
knowledge indicates for Sciara. In Sciara,
only the somatic cells conform in chromosome number to their expected phenotypes.
The germ cells show not only a regulated instability of their chromosome number but
the number is different from that of the
supporting somatic cells. The fact that sex
mosaics in Sciara may develop both an
ovary and testis in the same animal (Metz,
1938; Grouse, 1960a, b) shows localized
phenotypic sex determination occurring
fairly late in development rather than the
generalized determination that would occur if sex were established at fertilization.
The germ line chromosomal differentiation from that of the somatic tissue has
parallels in a number of fairly widely dispersed species. The significance of these
types to soma line determination and to the
reversibility or irreversibility of differential gene activation in differentiated cells
subsequent to embryogenesis has been considered by Beermann (1956). Although
these types are yet in the fringe areas of
our knowledge surrounding the general
paths taken in the evolution of sex determining mechanisms, they promise to have
more generality as clarification of gene action becomes more exact.
B. APIS AND HABROBRACON
Hymenopteran interi:)retations of sex determination have largely turned on studies
of the honey bee. Apis mellijera Linnaeus
and Habrohracon juglandis Ashmead. Dzierzon early established that the drones of
honey bees come from unfertilized eggs,
whereas the females, queens, and workers
come from fertilized eggs so that sex differ
entiation is marked by an N set of chromosomes for the male and 2N for the female.
This mechanism was satisfactory until it
was realized that on a balanced theory the
doubling of a set of chromosomes, if truly
identical, should not change the gene balance and consequently not the sex. Further
doubt was cast on the N-2N hypothesis for
sex determination by the discovery of diploid males by Whiting and "Whiting (1925).
These difficulties were resolved by Whiting
(1933a, b) with the suggestion that the two
genomes in the female were not truly alike
but actually contained a sex locus linked
with the gene for fused which was occupied
by different sex alleles as Xa and Xb . In
this A'iew the heterozygous condition would
lead to the production of females, whereas in
the haploid or homozygous condition either
of these genes would react to produce males.
Difficulties with this hypothesis became evident in that the ratios of males to females in
certain crosses were significantly divergent
from those which were expected. Evidence
was collected and trials made to interpret
these difficulties (Whiting, 1943a, b) by assuming that on fertilization by Xa-bearing
sperm the polar body spindle would turn
so as to cast out the Xa chromosome and retain the complementary Xb in the majority
of cases instead of in a random half. Snell
(1935) offered the hypothesis that there
could be several loci for sex genes, such that
the X locus might be a master locus, but
when this locus was in homozygous condition the sex would then be controlled by
genes in other loci in the genome. As pointed
out by Bridges (1939) this hypothesis would
satisfy that of sex gene balances postulated
in Drosophila and of change in emphasis on
loci for sex genes as observed by Winge
(1934) in Lebistes. However, the work of
Bostian (1939) called both hypotheses into
question. Consideration of these further results led to the multiple allele hypothesis of
complementary sex determination for
Habrobracon (Whiting, 1943a) taking a
similar form to that of the sterility relations
observed for a single locus in the white
clover of INIelilotus. Under this system the
sex locus would be occupied by multii)le alleles, any one of which or any combination
of identical alleles would be male-producing,
but any combination of two different al
FOUNDATIONS FOR SEX
83
Iclcs would l»e female determining. By having a sufficient number of these genes the
jiroduction of diploid males would be curtailed to a point at which their various frequencies could be explained. In support of
this liyi)othesis, multiple alleles to the number of at least 9 were found to exist for
thi.> single sex locus.
In principle at least, the honey bee could
have the Habrobracon scheme of sex determination. Rothenbuhler (1958) has recently collected the researches which test
this possibility. Tests of the multiple allele
hypothesis as applied to the honey bee were
made by Mackensen (1951, 1955) who interpreted evidence for inviable progeny produced by mating of closely related individuals as proof that this species as well as
Habrobracon juglandis follows the multiple
allelic system. The discovery of male tissue
of bii)arental origin in mosaic bees from related i)arents was considered as further evidence for the multiple allelic theory of sex
determination (Rothenbuhler, 1957).
Most recent cytologic evidence supports
the concept that there are 16 chromosomes
in the gonadal cells of the male and 32 in
those of the female (Sanderson and Hall,
1948, 1951; Ris and Kerr, 1952; Hachinohe
and Onishi, 1952; Wolf, 1960». Hachinohe
and Onishi (1952) found 16 chromosomes
as characteristic of the meiosis in the drone.
Wolf observed a nucleus in both bud and
spermatocyte of the only maturation (equational) division.
The greatest progress has been made in
understanding the mechanisms of sex mosaicism in the Hymenoptera species. These
mosaics, although ordinarily of rather rare
occurrence, have a direct bearing on sex
determination and development. In Apis,
iiolyspermy furnishes the customary basis
for their formation. One sperm fertilizes
the haploid egg nucleus and another sperm,
which has entered the egg instead of degenerating as it ordinarily does, enters into
mitotic cleavage and eventually forms islands of haploid cells of paternal origin
among the diploid cells derived from the
fertilized egg (Rothenbuhler, Gowen and
Park, 1952). Evidence showing that genetic
influences affect the sperm nucleus toward
stimulating its independent cleavage is
found to exist in Apis material (Rothen
buhler, 1955, 1958). Tliousands of gynandromorphs have been observed in Apis, all
but a small number of which have been produced in this manner. This method of initiating sex mosaics also exists for Habrobracon (Whiting, 1943b) but is rather rare.
In Habrobracon the frequent mode has a
different origin. The gynandromorph is
formed from the cleavage products of the
normal fertilization of the egg nucleus combined with those of a remaining nuclear
product of oogonial meiosis. Under these
conditions the female tissue is 2N of biparental origin and the male tissue is N of
maternal origin (Whiting, 1935, 1943b).
This type is less frequent in Apis but one
specimen has been described by Mackensen
(1951).
A number of other ways in which sex
mosaics may occur are occasionally expressed in these species. Three different
kinds of male tissue have been observed in
individual honey bee mosaics produced by
doubly mated queens — haploid male tissue
from one father, haploid male tissue from
the other genetically different father, and
diploid male tissue of maternal-paternal
origin. In other cases, the diploid, biparental
tissue was female and associated with two
kinds of male tissue (Rothenbuhler, 1957,
1958) . Cases where the haploid portions of
the sex mosaics are of two different origins,
one paternal and the other maternal, while
the female portion is representative of the
fertilized egg, are known in Habrobracon
(Whiting, 1943b). Similarly, Taber (1955)
observed females which were mosaics for
two genetically different tissues and which
he accounted for as the result of binucleate
eggs fertilized by two sperm. Mosaic drones
of yet another type were observed by
Tucker (1958) as progeny of unmated
queens. They were interpreted as the cleavage products from two of the separate nuclei formed in meiosis. These cases represent
a number of the possible types that arise
through meiotic or cleavage disfunctions
under particular environmental or hereditary conditions.
Tucker (1958) studied the method by
which impaternate workers were formed
from the eggs of unmated queens. For this
purpose he used genetic markers, red, chartreuse, ivory, and cordovan. Observations
34
BIOLOGIC BASIS OF SEX
Avore nuult' i)ii 237 workers from hotcrozygous mothers. For the chartreuse loeus. 12 to
20 per cent were homozygous, for x\w i\ory
locus 1.8 per cent, and (he cordovan locus
on lesser numbers per t-ent. An egg which
is destined to become an automictic worker,
a gynandromorph with somatic male tissue
or a mosaic male, is retained within the
queen for an unusually long time during
which meiosis is suspended in anaphase 1.
Normal reorientation of first division
spindle is i)ossibly inhibited by this aging
so that after the egg is laid meiosis II occurs
with two second division spindles on sejiarate axes as Goldschmidt conjectured for
rarely fertile rudimentary Drosophila
(19")7i. Two polar l)odies and two egg
prontich^i are formed. The polar bodies take
no fiu'ther part in develoinnent. In most of
the unusual eggs the two egg pronuclei
unite to form a diploid cleavage nucleus
which develops into a female. Rarely the
two egg pronuclei develop separately as two
haploid cleavage nuclei to form a mosaic
male. Two unlike haploid cleavage nuclei,
one descending from each of the two secondary oocytes after at least one cleavage
di\ision. unite to form a dijiloid cleavage
nucleus which develops together with the
remaintler of the haploid cleavage nuclei
to produce a gynandromorph with mosaic
male tissues. The male and female tissues
within these unusual gynandromor[ihs or
female types were identical with normal
drone or normal female tissues so were
probably haploid and diploid resiiectively.
Genetic segregation observed within the
mothers of automictic workers allows the
estimation of the distance between the locus
of the gene and its centromere. "With random
recombination and "central union" Tucker
estimates this distance for the chartreuse
locus to centromere as 28.8 units and for the
ivory to its centromere 3.6 units. Four lines
of bees of diverse origin all showed a low
percentage of automictic or gynandromorphic types produced from queens in each
line. Various chance environmental conditions apparently influence the rate of production of these types. However, there were
some females in two of the lines with higher
frequencies inciicating that innate factors
may have significant eft'ects on their frequencies. Observations on Drosophila spe
cies — I), porthenogeuetica (Stalker, 1956b),
I). ))ia)njabeirai (INIurdy and Carson, 1959)
and D. nielanogaster (Goldschmidt, 1957) —
strongly suppt)i-t this A-iew.
The [irohleni of si'x determination in Hal)rol)i'acon presently stands as a function of
multii)le alleles in one locus, the heterozygotes being female and the azygotes and
homozygotes male. The occasionally diploid
males are regularly produced from fertilized
eggs in two allele crosses after inbreeding.
These diploid males are of low viability and
are nearly sterile. Their few daughters are
triploids, their sperm being dijiloid. Apis
probably follows the same scheme, as a
few cases of mosaics with diploid male tissue are known and close inbreeding results
in a sufficient number of deaths in the egg
to account for diploid males which might be
formed. ^lormoniella (Whiting, 1958), however, shows that this scheme for sex determination does not hold for all Hymenoptera.
In this form diploid males may occur
through some form of mutation. They may
then develop from unfertilized eggs laid by
triploid females. In contrast to Habrobracon the dijiloid males are highly viable and
fertile. Their sperm are diploid and their
numerous daughters triploid. Virgin triploid
females produce 6 kinds of males, 3 haploid
and 3 dij^loid. Similarly ]\Ielittobia has still
a different and as yet unexplained form of
sex determination. Haploid eggs develop
into males. After mating many eggs are laid
which develop into nearly 97+ per cent females. The method of reproduction is close
inbreeding but no dijiloid males or "bad"
eggs are formed. The prol)lem of the sex
determining mechanism remains open
(Schmieder and Whitiuii, 1947).
The silkworm, Bomby.r mori, differs from
Drosophila, Lymantria and the species thus
far discussed in having a single region in the
^^' chromosome (Hasimoto, 1933; Tazima,
1941, 1952) occupied by a factor or factors
of high female potency. The strong female
potency has thus far been connnon to all
races. The chromosome patterns of the
sexes are like those of Abraxas and Lymantria: males ZZ + 2A and females ZwV 2A.
The diploid chromosome number is 56 in
both sexes. Extensive, well executed studies
FOUNDATIONS FOR SEX
35
liave revealed no W chruniosome loci for
genes expressed as morphologic traits. From
radiation-treated material it has been possible to pick up a translocation of chromosome II to the W chromosome as well as a
cross-over from chromosome Z. This chromosome together with tests of hypoploids
and hyperploids have materially aided in
understanding how the normal chromosome
complexes determine sex. The sex types resulting from different chromosome arrangements have been summarized by Yokoyama
1 1959) and are presented in Table 1.3.
Whenever the W chromosome was absent a male resulted. Extra Z or A chromosomes did not influence the result. Similarly
with a W chromosome in the fertilized egg
a female developed. Again extra Z or A
chromosomes did not influence the result.
A full Z chromosome was essential to survival. Hypoploids deficient for different
amounts of the Z chromosome in the presence of a normal W chromosome all died
without regard to the portion deleted. Hyperploids for the Z chromosome, on the other
hand, when accompanied with a W chromosome all lived and showed no abnormal sexual cliaracteristics. Parthenogenesis led to
the pioduction of both sexes, although the
males were more numerous than the females. Diploidy was necessary for the eml)ryo to go beyond the blastoderm stage.
Triploid and tetraploid cells were often
found. High temperature treatments led to
merogony (Hasimoto, 1929, 1934). The exceptional males were homozygous for a sexlinked recessive gene and were explained
by assuming that the egg nuclei were inactivated by the high temperature and
the exceptional males developed from the
union of two sperm nuclei. This conclusion
was supported by cytologically observed
l)olyspermy (Kawaguchi, 1928) and by
cytologic observation of the union of two
sperm nuclei by Sato ( 1942 ) . Binucleate eggs
were also believed to occur, which when
fertilized by different sperm may each construct half of the future body. This type of
mosaicism was influenced by heredity
iGoldschmidt and Katsuki, i927, 1928,
1931 ). Polar body fertilization was also believed to occur, one side of the embryo originating from the ordinary fertilized egg nucleus and the other side from the union of
TABLE 1.:^
Sex in Bombyx iitori
(Summarized by T. Yokoyama, 1959.)
Sex
Chromosome Types and Numbers
W
z
A
Male
W
II.W.ZL
w
w
WW
WW
zz
zz
zzz
z
z
zz
zzz
zz
zz
AA
Male
Male
Female
Female
Female
Female
Female
Female
AAA
AAA
AA
AA
AAA
AAAA
AAA
AAAA
nuclei of two of the polar bodies. Similarly,
dispermic merogony was noted following
the formation of one part of the body from
the fertilization nucleus, the other part from
the union of two sperm nuclei, the result
being a gynandromorph or mosaic.
VI. Sex Determination in Dioecious
Plants
\. MELAXDRUM t LYCHNIS]
Over the last 20 years studies on several
species of dioecious plants have made notable advances in unclerstanding the mechanisms by which sex is determined.
Melandrium album has been shown to
have the same chromosome arrangement as
Drosophila. The male has an X and Y plus
22 autosomes, whereas the female has XX
plus 22 autosomes. Sex-linked inheritance
is known for genes borne in the X chromosomes as well as for genes born in the Y
chromosome. The X and Y chromosomes
are larger than any of the autosomes with
the Y chromosome about 1.6 times that of
the X in the materials studied by Warmke
( 1946) . Separate male and female plants are
characteristic of the species. By use of
colchicine and other methods, Warmke and
Blakeslee (1939), Warmke (1946), and
Westergaard (1940) have made various
l^olyploid types from which they could derive other new X, Y and A chromosome
combinations from which information was
obtained on the location of the sex determining elements. The Y chromosome carries
the male determining elements, the X chro
36
BIOLOGIC BASIS OF SEX
mosome the female determining elements.
The guiding force of the elements in the Y
chromosome during development is sufficient to override the female tendencies of
several X chromosomes. Data derived by
each of these investigators are shown in
Table 1.4.
From these data Warmke (1946) concluded that the balances between the X and
the Y chromosomes essentially determined
sex with the autosomes of relatively little
importance. Where no Y chromosomes were
present but the numbers of X chromosomes
ranged from 1 to 5, only females were observed, even though the autosomes varied in
number from two to four sets. When a Y
chromosome was present the individual was
of the male type unless the Y was balanced
by at least 3 X chromosomes when an occasional hermaphroditic blossom was formed.
TABLE L4
Numhers of X, Y, chromosomes and A, autosome sets
and the sex of the various Melandrium plants
(Data from H. E. Warmke, 1946; and
M. Westergaard, 1953.)
Ratio
Chromosome
Warmlce
Westergaard
Constitution
X/A
4A 5X
Female
1.3
4A 4X
Female
1.0
Female
4A 3X
Female
0.8
4A 2X
Female
0.5
3A 3X
Female
1.0
Female
3A 2X
Female
0.7
Female
2A 3X
Female
1.5
2A 2X
Female
1.0
Female
Bisexual*
X/Y
4A 4X Y
4.0
Male
4A 3X Y
Malet
3.0
Male
4A 2X Y
Malet
2.0
Male
4A X Y
Male
1.0
3A 3X Y
Malet
3.0
3A 2X Y
Malet
2.0
Male
3A X Y
Male
1.0
2A 2X Y
Malet
2.0
2A X Y
Male
1.0
Male
4A 4X YY
Malet
2.0
4A 3X YY
Male
1.5
4A 2X YY
Male
1.0
Male
2A X YY
Male
0.5
- Occasional staminate but never carpellate
blossom.
t Occasional licrina])hr(i(lit ic blossom.
When 4 X chromosomes were present together with a Y, the plants were hermaphroditic but occasionally had a male blossom.
Two Y chromosomes almost doubled the
male effect. Two Y chromosomes balanced
4 X chromosomes to give a majority of male
plants. Only an occasional plant showed an
hermaphroditic blossom. Autosomal sex
effects, if present, were only observed when
plants had 4 sets and 3 or 4 X chromosomes
balanced by a Y chromosome. Warmke used
the ratio of the numbers of X to Y chromosomes as a scale against which to measure
clianges from complete male to hermaphroditic types. No mention is made of quantitative measures of the sex character changes
with increasing X chromosome dosages.
This is of interest since in many forms
changes in chromosome balance are accompanied by changes of phenotype which are
unrelated to sex. That such phenotypic
changes do accompany changes in autosomal
balance in Melandrium are proven, however, by further observations of Warmke in
4 trisomic types coming from crosses of
triploids by diploids. Of 36 such trisomies
analyzed, 5 or 6 of them were of different
growth habits and morphologic types. These
differences did not affect the sex patterns
since all were females. Warmke and Blakeslee in 1940 observed an almost complete
array of chromosome types from 25 to 48 in
progeny derived from crosses of 3N x 3N,
4N X 3N, and 3N x 4N. Out of about 200
plants studied, only 4 were found to show
indications of hermaphroditism. These types
were 2XY and 3XY. As noted from the
table, even the euploid plants would occasionally be expected to have an hermaphroditic blossom. Of the 200 plants, all with a
Y (XY, 2XY, 3XY) were males and all
plants without the Y (2X, 3X, 4X) were
females. In an 8-year period up to 1946.
Warmke was able to observe only one male
trisomic. From these facts he concluded
that the autosomes are unimportant in the
sex determining mechanism utilized by this
species. In their crosses they were unsuccessful in getting a 5XY plant, the point at
which the female factor influence of the X
chromosomes might be expected to nearly
equal or slightly surpass that of the single
Y. From the j^hysiologic side the obscrva
FOUNDATIONS FOR SEX
37
tion of Strassburger in 1900, as quoted by
both Warmke and Westergaard, that the
fungus Ustilago violacea when it infects
Melandrium will cause diseased plants to
produce mature blossoms with well developed stamens (filled with fungus spores) as
well as fertile pistils, shows that these females have the potentialities of both male
and female development. The case suggests
that sex hormone-like substances may be
produced by the fungus which acting on the
developing Melandrium sex structures
cause sex reversions. Should this be true,
Melandrium cells would have a parallel
with those of fish where sex hormones incor|)orated in the developing organism in sufficient quantities can cause the soma to
develop a phenotype opposite to that expected of their chromosomal type. For other
aspects see Burn's chapter and Young's
chapter on hormones.
Westergaard's studies (1940) with European strains of Melandrium were in progress at the same time as those of Warmke
and Blakeslee. In their broad aspects both
sets of data are concordant in showing the
l^rimary role of elements found within the
Y chromosome in determining the male sex
and of elements in the X chromosomes for
the female sex. Examination of Table 1.4
shows that the strain used by Westergaard
has a Y chromosome containing elements of
greater male sex potentialities than the
strain used by Warmke.
A similar difference appeared in the sex
potencies of the autosomes of European
strains. Instead of obtaining essentially
only male and female plants in crosses involving aneuploid types, Westergaard obtained from 3N females (3A + 3X) x 3N
males (3A + 2XY) 10 plants which were
more or less hermaphroditic, 21 females, and
15 males. Studies of the offspring of these
hermaphrodites through several generations
showed that their sex expression required
effects by both the X chromosomes and certain autosome combinations which under
special conditions counterbalanced the female suppressor in the Y chromosome. Increasing the X chromosomes from 1 to 4
increased the hermaphrodites from to 100
per cent in the presence of a Y chromosome.
However, in euploids these types would be
all males. The significance of the autosomes
is further shown by the fact that among 205
aneuploid 3XY plants, 72 were males and
133 were hermaphrodites.
As pointed out for Drosophila, quantitative studies on the effects of sex chromosomes and autosomes in Melandrium are
handicapped by not having a suitable scale
for the evaluation of the different sex types.
The data presented by Westergaard and by
Warmke make this difficulty become particularly evident. In the interest of quantizing
the X, Y, and A chromosome on sex the
author has assigned a value of 1 for the
male type, 3 for the female type, and 2
when the types are said to be hermaphroditic. When the types are mixed, as for example, in the data of Warmke where he says
a particular type is male with a few blossoms, the type is assigned a value of 1.05 or
1.10, depending on the numbers of these
blossoms. His bisexual type which comes
as a consequence of Y, 4X and 4A chromosome arrangement is given a value of 2, although possibly the value should be somewhat higher as it may well be that the fully
bisexuals are further along in the scale toward female development than the hermaphroditic types. The data are treated on the
additive scale both as between chromosomal
types and within chromosomal type. This is
apparently unfair if we examine the work
of Westergaard in which it looks as if particular autosomes rather than autosomes in
general make a contribution to sex determination. The results, when these methods are
used, are as follows:
Westergaard in Tables 1 to 5 of his 1948
paper gives information on sex types with
a determination of the numbers of their
different kinds of chromosomes. Analysis
of these data by least square methods shows
that the sex type may be predicted from
the equation
Sex type = - 1.37 Y + 0.10 X
+ 0.01 A + 2.34
This equation fits the data fairly well considering that the correlation between the
variables and the sex type is 0.87. This
analysis again shows that the Y chromosome has a strong effect toward maleness.
The X chromosomes are next in importance
38
BIOLOGIC BASIS OF SEX
with an effect of each X only about 1/13
that of the Y and in the direction of femaleness, the autosomes have one tenth the effect
of the X chromosomes but they too have
a composite effect toward femaleness. It is
to be remembered that the Y chromosome
variation is limited to 2 chromosomes
whereas the X chromosomes may total 4,
and the autosomes may range from 22 up
to 42, so that the total effect of the autosomes is definitely more than their single
effects. These data are for aneuploids. Examining Westergaard's data for 1953 for the
euploids and assigning the value of 1.5 for
the type observed when there was one Y
chromosome, four X, and four sets of autosomes, we have the following equation:
Sex value = -1.29 Y + 0.10 X - 0.01
(autosome sets) + 2.53
In these data, as distinct from those above,
the autosomes are treated as sets of autosomes since they are direct multiples of each
other so the value of the individual autosome is but 1/11 that given in the equation.
This equation shows no pronounced difference from that when the aneuploids were
utilized. The Y chromosomes have slightly
less effect toward the male side. The X
chromosomes have practically identical effects but there has been a shift in direction
of the autosomal effects on sex, although
the value is small. The constants are subject to fairly large variations arising
through chance.
In Table 10 of Westergaard's 1948 paper
he presented data on the chromosome constitution and sex in the aneuploids which
carried a Y chromosome. These data are of
particular interest as the plants are counted
for the i)roi)ortions of those which are male
to those which are hermaphroditic. The
plants with a Y chromosome plus an X are
all males. Those which have either one, two
or three Y chi'omosomes balanced by two
X chromosomes have 89 per cent males.
The plants with three X chromosomes and
one oi- two Y's have 36 p(T cent males and
those which have one or two ^■ chroiiiosoincs
and four X chromosomes have no males.
The woik iiiv()l\-cd in getting these data is,
of course, large indeed and is definitely
handicapped by the diiiicuHies in obtaining
certain types. Thus the XXYYY and the
4X + 2Y types depend only on one plant.
There are eight observations but the fitting
of the data for the X and Y constitutions
eliminates three degrees of freedom from
that number so that statistically the observations are few. The data do have the advantage that the sex differences can be
measured on an independent quantitative
scale. The equation coming from the results
is:
Percentage of males = 13.2 Y - 36.4 X
+ 134.4
These results show that the Y chromosome
increases the proportion of males and the
X chromosome increases the proportion of
intersexes. The data are not comparable
with those analyzed earlier as these data
are describing simply the ratio between the
males and intersexes, instead of the relations betw'een the males, intersexes, and females. The equation fits the observations
rather well, as indicated by the fact that
the correlation between the X's and Y's
and the percentages of males is 0.98, but
there are large uncertainties.
As a contrast to these data we have those
presented by Warmke (1946) in his Tables
2 and 3. These data give the numbers of X
and Y chromosomes found within the plants
but not the numbers of autosomes, the autosomes being considered as 2, 3, and 4 genomes. Analyzing these data in the same
manner as those of Westergaard's Table 1,
we find that the
Sex type = -1.05 Y + 0.22 X -0.04 A
-f2.25
As indicated for Westergaard's data, the A
effect is now in terms of the diploid type
e(iualing 2, the trijiloid 3, and the tetral)loid 4.
The Y chromosome has a i)ronounccd effect toward maleness, the effect l)eing someW'hat less in Warmke's data than that of
Westergaard's. The X chromosomes on the
other hand, have nearly twice the female
infhience in Warmke's data that they do in
the phiiits grown by Westergaartl. A difference in sign exists for the effect of the A
rhi'oinosnnie genom(\s as well as a difference
in [\\v (|uantitati\'e effect. Th(^ values for
FOUNDATIONS FOR SEX
39
both sets of data are small and toward the
male side. As Westergaard points out, the
strains used by these investigators are of
different geographic origins. The evolutionary history of the two strains may have a
bearing on the lesser Y and greater X effects on the sex of the American types.
Chromosome changes seem to have occurred
in the strains before the studies of Warmke
and Westergaard and will be discussed.
The location of the sex determiners has
been studied by both investigators utilizing
techniques by which the Y chromosome becomes broken at different places. These
breakages may occur naturally and at fairly
high rates in individuals which are Y + 2X
+ 2A. These facts suggest that the breakage of the Y chromosome occurs in meiosis
since the breakage comes in selfed individuals of highly inbred stocks where heterozygosity is not to be expected, in the Y
chromosome which has no homologue thus
does not synapse, and in the second meiotic
eriments with fowl pox it has been
shown that the number of eggs developing
parthenogenetically increases considerably
following vaccination. The factors leading
to parthenogenesis are considered to be the
genetic characteristics of the strain of birds
and the presence of an activating agent or
agents in the blood stream of the hens.
The parthenogenetic forms are of particular interest to the problem of sex determination. The females should l)e producing two
types of oocytes Z -I- A and W -h A of
which presumably the Z + A alone survive
since the embryos capable of being sexed
are all males. The embryos are also diploids.
The 2Z -I- 2A could be derived from a fusion
of the Z -H A polav body nuclei as noted
earlier or possibly chromosome doubling
coming later in the early cleavage. A genetic element seems partially to control the
parthenogenetic process. Chromosome doubling would lead to cells with identical pairs
of chromosomes. The gene would be homozygous. Inbreeding of poultry leads to a continning and rai^id loss in the vialiility of
FOUNDATIONS FOR SEX
49
most strains of chickens. A greater loss
would be expected for truly homozygous
chickens or poults as birds are known for
the large numbers of sublethal genes they
carry. In fact, it is surprising that any survive to the adult stage.
The doubling of the W and A type would
result in individuals lacking the Z chromosome. From what was observed in Amphibia
and fish the WW + 2A, individual if it
survived, would be expected to be female.
Since this type has not as yet been detected
it may be inferred that it is inviable because of loss of certain essential genes in the
Z chromosome.
X. Sex Determination in Mammals
A. GOAT HERMAPHRODITES
Goat hermaphroditism as reported by Asdell (1936), Eaton (1943, 1945) and Kondo
(1952, 1955a, b) is of particular interest
when comjjared with human hermaphroditism as observed by Overzier (1955) and of
testicular feminization as reported by Jacobs, Baikie, Court Brown, Forrest, Roy,
Stewart and Lennox (1959) and others.
In each species the phenotypic range in sexual development extended from nearly perfect female to nearly perfect male, with the
most frequent class as an intermediate. External appearance of each was partially correlated with internal structure. When internal female structures as the INIiillerian ducts
were present, the external appearance was
more female-like. When the male structures
AVolffian ducts were developed, the external
api^earance was more male-like. The presence of the dual systems within certain of
these hermaphroditic types indicates, as in
Drosophila, that there is independence of
development of each system without a socalled turning point calling for differentiation of the female sex followed by that of
the male sex or vice versa.
In goats the hermaphroditic types were
traced to the action of a recessive autosomal
gene (Eaton, 1945; Kondo, 1952, 1955a, b).
This gene apparently acts only on the female zygote. In homozygous condition the
eml)ryos bearing them develop simultaneously toward the male as well as toward the
female types. This development resembles
closely that of the Hr gene in Drosophila,
because, although Hr is dominant and the
one in goats is recessive, they both operate
only on the female type and both tend to
develop jointly both male and female systems in sexual development.
One jarring note comes in relating the
cytologic basis for sex determination in
goats with that for the intersexes. The sex
ratios for the different crosses clearly place
the hermaphrodites as genetic females expected to have the XX chromosome constitution. The XX constitution would then
also agree with that found for human
hermaphrodites as discussed later in this
paper. Makino (1950) has shown for one
case of the intersexual goat that its sex
chromosomes were of the male type. Makino's excellent studies with other species
made this observation of particular significance as it was contrary to the other morphologic and genetic evidence on these
hermaphrodites. The implications were fully
realized by Makino when the cytologic observations were made so that as far as possible the observations should be critical on
this point. However, there are several
sources of cell variation that suggest the
desirability of further checks. The chromosome number of the goat is large, normal
mitoses rarely appear in the gonads of the
intersexes, and the chromosomes of the
goat's spermatogenesis are so small as to
make difficult details of structure or identification. Some of the difficulties possibly
could be avoided by making tissue cultures
and determining the somatic chromosome
numbers of their cells.
Kondo (1955b) has shown that under the
breeding conditions of Japan when the sire
was heterozygous, the percentage of intersexes actually approached the expected
value 7.3 per cent. When the sires were
homozygous recessive individual matings
showed 14.6 per cent hermaphrodites as was
expected. Continued mating of homozygotes
should show 25 per cent of the total kids
hermaphrodites, or the equivalent of 50 per
cent of the female progeny.
Hermaphroditism in goats has a further
advantage in that the locus is apparently
linked closely to the horned or polled condition. The horned condition, in consequence,
becomes a valuable indicator marking the
presence of the hermaphroditic factor in the
50
BIOLOGIC BASIS OF SEX
otherwise indistinguishable male types.
With these characteristics the goat types
have remarkable advantages over other
species for the solution of problems of
hermaphroditism.
The gene for goat hermaphroditism has
even more interest when it is contrasted
with that of another gene, tra, discovered
by Sturtevant (1945). Tra is recessive wdth
no distinguishable heterozygous effect. In
the homozygous state it converts the zygotic
female into a form with completely male
genitalia and internal reproductive tract
with no evidence of the female sexual reproductive system. The gene effects in Drosophila are more extreme than those in
goats but are concordant in showing that
there are loci in the autosomes which may
be occupied by recessive genes having direct
effects on phenotypic development of the
genotypic female. This evidence indicates
the significance of these genes rather than
the happenstance of their being in the
autosome, X or Y chromosome.
B. SEX IN THE MOUSE
The mouse has the XY + 38 A chromosomal arrangement for the males and XX +
38 A for the females. Similar karyotype patterns have been reviewed for some Amphibia
and fish. Other Amphibia and fish may have
their karyotypes reversed as both forms are
found in nature or observed in breeding
studies. Similar reversals may be made experimentally in the phenotypes even though
the genotypes remain unaltered. Birds show
the sex differentiating arrangement of ZW
for the females and ZZ for the males. Parthenogenesis seems to lead to males of ZZ
type in domestic fowl and turkeys. In an
evolutionary sense the mammals could have
originated from and perpetuated either of
the major karyotype sex arrangements.
Mice and men are alike in that the X has
female-determining properties and the Y
male potencies. How much part the genes in
the autosomes have in sex develojoment is
not yet clear. Welshons and Russell (1959)
have shown that mice of the presumed X()
constitution are females and arc fertile.
They have 39 as the modal number of
chromosomes found in their bone marrow
cells, wiiereas the genetically proven XX
types have 40 cln'omosomcs. X ('hroinosoinc
linked genes' behavior substantiate the
chromosomal constitutions of XO and XX
as females and XY as males.
These results are further supported by the
breeding behavior of the X-linked recessive
gene, scurfy (Russell, Russell and Gower,.
1959). This gene is lethal to the hemizygous
males before breeding. The genetics of the
scurfy females have been analyzed by transplanting the ovaries to normal recipient females and obtaining offspring from them. In
the scurfy stock the XO type occurred as 0.9
per cent of the progeny. The YO progeny
w^ere not identified and probably die prematurely. Nondisjunction of the X and Y
chromosomes in the males could result in
sperm carrying neither X nor Y chromosomes. These sperm on fertilization of the
X egg would give an XO + 2A type individual. Because the result is a female, this
would support the Y chromosome as of male
potency. The mouse arrangement may then
be expected to be like Melandrium in which
a well worked out series of types is known.
Sex ratio in mice is strain dependent over
what has thus far proven to be a 10 to 15
per cent range. Weir (1958) has shown that
for two strains of mice established by selecting for low and high pH, the sex ratio figures
were 33 and 53 per cent for artificially inseminated mice and 41 and 52 per cent for
natural matings of these respective strains.
The differential pH values for the bloods of
the low line were 7.498 ± 0.006 and for the
high line 7.557 ± 0.007 as of the sixth
generation of selection. The parents with
the more alkaline bloods tended to have
greater percentages of males in their progenies. These results direct attention to the
genotype dependent phenotypic factor
which may be of some importance for
variations in sex ratios.
C. SEX AND STERILITY IN THE CAT
The tortoiseshell male cat has long interested geneticists because it has seemed that
by theory it should not be. However, nature
has wonderful ways of circumventing best
laid hypotheses, sometimes when they are
fals(\ sometimes when they have not been
probed dee])ly enough. The yellow gene for
coat color in cats is sex-linked. This gene
operates on an autosomal background of
^(■lu's for black oi' tabby. Tlu^ females may
FOUNDATIONS FOR SEX
51
be phenotypically orange as the double dose,
0/0, covers up the effects of the other coat
color genes; or tortoiseshell, 0/+; or black
or tabby, +/+. The males may be orange,
'0/, black or tabby, +/, and the type unexpected tortoise. The tortoiseshell males are
timid, keep away from other males, and are
generally sterile. Testes are of much reduced
size and solid consistency. Exceptionally,
tortoiseshell males may mate and offspring
presumed from the matings may be born.
Active study of these males commenced as
early as 1904. Komai (1952) has offered a
unified hypothesis for their origin. Komai
and Ishihara (1956) have contributed added
information and a review of the literature
to which the reader is referred.
The cat has 38 chromosomes including an
X-Y pair for the males. The tortoise males
agree in having this arrangement (Ishihara,
1956) , the X being 3 or 4 times the length of
the Y in all cytologic preparations from
Japanese cats. Komai (1952) visualizes the
cat X chromosomes as composed of a pairing
segment containing the kinetochore and gene
loci among which is that for the orange gene
and a differential segment, not found in the
Y chromosome, containing the factor-complex for femaleness. The Y chromosome is
visualized as having a segment containing
the kinetochore and capable of pairing with
the X chromosome. This segment may cross
over with the X so that it may acquire the
locus for orange or its wild type. The Y
chromosome is viewed as containing two
differential segments. The one carrying the
factor complex for maleness is located to
correspond with the X differential segment
carrying the female sex factor. The second Y
differential segment is at the other end of the
chromosome and contains the male fertility
complex. The tortoiseshell sterile males are
interpreted as caused by a Y chromosome
crossing over with the X chromosome to incorporate the male segment and the gene
in the resulting Y chromosome but with the
loss of the male fertility segment. The gamete carrying this modified Y fertilizing an
egg with a normal X chromosome containing
the wild type instead of the gene develops
into the sterile tortoiseshell male. The data
show that the probability of these events occurring is small. Komai records as reliable
■65 tortoiseshell male cats where the inci
dence of the O gene in the whole population
of Japanese cats is 25 to 40 per cent. Of the
65, 3 were apparently fertile. These cases
and the few others found in the literature are
regarded as caused by those rare occasions
when the Y chromosome incorporates the
gene but retains the male fertility complex
as might occur in double crossing over. The
hypothesized factor locations and crossing
over arrangements also may explain the unexpected black females which are known to
occur in some matings. Although not mentioned, black males and orange males showing the same sterility features as the sterile
tortoiseshell males should also be found in
the cat poi)ulation. If found they would
further strengthen the hypotheses.
It is difficult to understand why, even with
its low initial frequency, the fertile tortoiseshell male would not establish itself in the
Japanese cat population, inasmuch as they
are so admired and sought after by all the
people if any tortoiseshell males became as
fertile as the tortoiseshell male "lucifer"
(Bamber and Herdman, 1932) known to
have sired 56 kittens.
Ishihara's work (1956) seems to close the
door on another attractive hypothesis to explain the origin of these unexpected cat
types. Tortoiseshell male reproductive organs include small, firm testes showing reduced spermatogonial development. Together with the interaction of the gene
with the wild type allele they suggest the
human types XXY + 2A which may arise
from nondisjunction. However, the chromosome type is shown to be XY -f- 2A = 38
which is fatal to this hypothesis.
It is of interest that Komai in 1952 postulated the male complex and fertility factors
in the Y chromosome of a mammal. The case
has a further parallel in the plant Melandrium in that the work of both Westergaard
(1946) and Warmke (1946) indicated the
Y chromosomes of this plant to contain such
factor complexes although in differing arrangements.
D. DEVIATE SEX TYPES IN
CATTLE AND SWINE
As a caution in the mushrooming of cytologic interjiretations of sex development, attention may be directed to the freemartin
types known particularly from the work of
52
BIOLOGIC BASIS OF SEX
Keller and Tandler (1916), Lillie (1917),
and the researches stimulated by their observations on cattle twins. The freemartin
in cattle develops in the same uterus with its
twin male. The blood circulations anastomose so that blood and the products it contains are common to both fetuses during development. The development of the female
twin is intersexual, presumably because of
substances contributed by the male twin to
the common blood during uterine growth.
The freemartin intersexuality may be graded
into perfectly functioning fertile females to
types with external female genitalia and
typically male sex cords except germ cells
are absent, vasa efferentia, and elements of
the vasa deferentia. The conditions are similar to those discussed for amphibia, fish, and
rabbits in which early sex development
passes through neutral stages during which
it may be directed toward one sex or the
other by the right environmental stimuli.
Intersexes in swine have been interpreted
as owing to similar causes (Hughes, 1929;
Andersson, 1956) although the resulting
phenotypes may not be quite as extreme.
The resulting intersexes for both cattle and
swine presumably are not caused by chromosomal misbehavior but to the right environmental stimuli operating on suitable gene
backgrounds. The observations of Johnston,
Zeller and Cantwell (1958) on 25 intersexual
pigs all from one breeding group of Yorkshires suggest significant inheritance effects.
The intersexes were of two types, "male
pseudohermaphrodites" and "true hermaphrodites," but there was some intergrading of
their phenotypes suggesting that they may
be the products of like causes. Common organs between the two groups included uteri,
vulvae, vaginae, testes, epididymis, and
penis or enlarged clitori. The "true hermaphrodites" were separated on the basis of no
prostates, bulbo-urethral glands, or seminal
vesicles as well as having testes or ovotestes
with ovaries. A similar case was described
by Hammond (1912) but, as in one of the
above cases, the supposed ovaries when sectioned seemed to be lymphatic tissue. Favorable nerve tissue^ from 6 of the Yorkshire
pigs was examined foi- nuclear chromatin.
The cases were found chromatin positive.
Phenotypically these cases also have parall(>ls in mice and man.
E. .SEX-iN man: chromosomal basis
A surprise even to its discoverers, Tjio
and Levan (1956), came with the observation that the somatic number of chromosomes in cultures of human tissue was 46
rather than the previously supposed 48.
Search for the true number has been going
on for more than half a century. In early
investigations the numbers reported varied
widely. Difficulties of proper fixation and
spreading of the chromosomes of human
cells accounted for most of this variation
and the numerous erroneous interpretations.
Among the observations that of de Winiwarter (1912) was of particular interest in
showing the chromosome number as 46
autosomes plus one sex chromosome with
the Y being absent. This number was also
found later by de Winiwarter and Oguma
(1926). Observations by Painter (1921,
1923) showed 46 chromosomes plus an X
and a Y, a total of 48. This number was
subsequently reported by a series of able
investigators, Evans and Swezy (1929),
Minouchi and Ohta (1934), Shiwago and
Andres (1932), Andres and Navashin
(1936), Roller (1937), Hsu (1952), Mittwoch (1952), and Darlington and Haque
(1955). As Tjio and Levan indicated, the
acceptance of 48 as the correct number,
with X and Y as the sex chromosome
arrangement, was so general that when
Drs. Eva Hanson-Melander and S. Kullander had earlier found 46 chromosomes
in the liver cells of the material they
were studying they temporarily gave up the
study. In the few years since 1956, the acceptance of 46 chromosomes as the normal
complement of man has become nearly
universal. There are 22 paired autosomes
plus the X and Y sex chromosomes.
The reasons which have warranted this
change of viewpoint are no doubt many,
but three improvements in technique are
certainly significant. The first came as a
consequence of simplifying the culture of
human somatic cells. The second followed
Hsu's (1952) recognition that pretreatment
of these cells before fixation with hypotonic
solutions tended to better spreads of the
chromosomes on the division plates when
subsefiuently stained by the squash techniciuo. Pretreatment of the cultures with
FOUNDATIONS FOR SEX
53
colchicine made the studies more attractive
by increasing the numbers of usable cells
that were in the metaphase of cell division.
Ford and Hamerton (1956) in an independent investigation, closely following
that of Tjio and Levan, observed that the
human cell complement contained 46 chromosomes. They, too, agreed with Painter
and others that followed him that the male
was XY and the female XX in composition.
A flood of confirming evidence soon followed: Hsu, Pomerat and Moorhead (1957),
Bender (1957), Syverton (1957), Ford,
Jacobs and Lajtha (1958), Tjio and Puck
(1958), Puck (1958), Chu and Giles (1959),
and a number of others.
In most instances the results of the different investigators were surprisingly consistent in showing that the individual cell
chromosome counts nearly always totaled
46. This was no doubt due in part to the
desirability of single layers of somatic cells
for identifying and separating the different
chromosomes into distinct units. Chu and
Giles' results illustrate this consistency.
For 34 normal human subjects, including
29 American whites and 4 American Negroes, and one of unknown race, and regardless of sex, age, or tissue, the diploid
chromosome number of the somatic cells
was overwhelmingly 46. In only five individuals were other numbers observed in
isolated cells. Out of 620 counts, 611 had
46 chromosomes; two individuals, whose
majority of cells showed 46, had 3 cells with
45 chromosomes; three other individuals,
the majority of whose cells showed 46, had
6 cells with 47 chromosomes. Average cell
plates counted per individual was nearly 20.
The only recent observations at variance
with these results were those of Kodani
(1958) who studied spermatogonial and
first meiotic metaphases in the testes from
15 Japanese and 8 whites. In these studies
at least several good spermatogonial metaphases in which the chromosomes could be
counted accurately, and secondly at least
15 spermatocyte metaphases in which the
structure of individual chromosomes could
be observed clearly, were made on each
specimen. The numbers of cells studied in
metaphase were generally above these numbers, one reaching 60 metaphases. Some variation was noted within individuals. Among
individuals, numbers of 46, 47, and 48 were
observed. Among 15 Japanese, 9 had 46, 1
had 47, and 5 had 48 chromosomes, whereas
among the whites 7 had 46, and 1 had 48.
Sixteen of the 23 individuals had 46 chromosomes. Karyotype analyses indicated
that the numerical variation was caused by
a small supernumerary chromosome. On the
basis of these observations it would appear
that individuals within races may vary in
chromosome number and yet be of normal
phenotype. However, in view of the extensive observations by others, it seems unlikely that the variation between individuals is as large as that indicated. It will
require much further study to establish any
other number than 46 as the normal karyotype of man. This is particularly true in
view of the work of Makino and Sasaki
(1959) and Alakino and Sasaki cited by
Ford (1960), in which they studied the human cell cultures of 39 Japanese and found
without exception 46 chromosomes, and the
earlier work of Ford and Hamerton (1956)
on spermatogonial material where they, too,
found 46 chromosomes in that tissue. The
best features of these human chromosome
studies will come in the identification of
the individual chromosomes making up the
human group. The chromosome pairs may
be ordered according to their lengths. The
longest chromosome is about 8 times the
length of the smallest. The chromosomes
may be classified according to their centromere positions. The chromosomes are said
by most observers to be fairly easily separated into 7 groups. Separation of the individual chromosome pairs from each other
and designation of the pairs so that they
can be identified by trained investigators
in all good chromosome preparations is not
possible according to some ciualified cytologists and admitted difficult by all students.
However, standardized reporting in the
rapidly growing advances in human cell
studies should refine observations, reduce
errors, and encourage better techniques.
With this in mind, 17 investigators working
in this field met in Denver in 1959 in what
has come to be called the "Denver conference" (Editorial, 1960). From an examination of the available evidence on chromosome morphologies an idiogram was set up
as a standard for the somatic chromosome
54
BIOLOGIC BASIS OF SEX
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Fig. 1.1. Id
r number, th
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FOUNDATIONS FOR SEX
55
complement of the normal human genome.
A reproduction of this standard is presented
in Figure 1.1, as kindly loaned by Dr. Theodore T. Puck for this purpose.
The autosomes were first ordered in relation to their size and such attributes as
would help in their positive identification.
Numbers were given to each chromosome as
a means of permanent identification. Basically, identification is assisted by the ratio
of the length of the long arm to that of the
short arm; the centromeric index calculated
from the ratio of the length of the shorter
arm to the whole length of the chromosome ;
and the presence or absence of satellites.
Classification is assisted by dividing the
chromosome pairs into seven groups.
Groups 1-3. Large chromosomes with approximatel}^ median centromeres. The
three chromosomes are readily distinguished from each other by size and
centromere position.
Group 4-6. Large chromosomes with submedian centromeres. The two chromosomes are difficult to distinguish, but
chromosome 4 is slightly longer.
Group 6-12. Medium sized chromosomes
with submedian centromeres. The X
chromosome resembles the longer chromosomes in this group, especially chromosome 6, from which it is difficult to
distinguish. This large group is the one
which presents major difficulty in identification of individual chromosomes.
Group 13-15. INledium sized chromosomes
with nearly terminal centromeres ("acrocentric" chromosomes). Chromosome
13 has a prominent satellite on the
short arm. Chromosome 14 has a small
satellite on the short arm. No satellite
has been detected on chromosome 15.
Group 16-18. Rather short chromosomes
with approximately median (in chromosome 16) or sul>median centromeres.
Group 19-20. Short chromosomes with approximately median centromeres.
Group 21-22. Very short, acrocentric chromosomes. Chromosome 21 has a satellite on its short arm. The Y chromosome belongs to this group.
Separations of the human chromosome
pairs into the seven groups is not as difficult
as designating the pairs within groups
(Patau, 1960). The svstem is a notable ad
vance in summarizing visually the current
information in the hope that availability of
such a standard will promote further refinements, lessen misclassification, and contribute to a better understanding of the problems
by cytologists and other workers in the field.
1. Xuclear Chromatin, Sex Chromatin
Sexual dimorphism in nuclei of man
(Barr, 1949-59) and certain other mammals
may be detected by the observable presence
of nuclear chromatin adherent to the inner
surfaces of the nuclear membrane. The material is about 1 /x in diameter. It frequently
can be resolved into two components of
equal size. It has an affinity for basic dyes
and is Feulgen and methyl green positive.
Nuclear chromatin can be recognized in 60
to 80 per cent of the somatic nuclei of females and not more than 10 per cent of
males. It is known to be identifiable in the
females of man, monkey, cat, dog, mink,
marten, ferret, raccoon, skunk, coyote,
wolf, bear, fox, goat, deer, swine, cattle, and
opossum, but is not easily usable for sex
differentiation in rabbit and rodents because these forms have multiple large particles of chromatin in their nuclei. The tests
can be made quickly and easily on skin
biopsy material or oral smears. Extensive
utilization of the presence or absence of
nuclear chromatin in cell samples of man
has been made for assigning the presumed
genetic sex to individuals who are phenotypically deviates from normal sex types.
(See also chapters by Hampson and Hampson, and by Money.) Numerous studies on
normal individuals seem to support the
test's high accuracy. However, in certain
cases involving sexual modification, questions have arisen which are only now being
resolved. In male pseudohermaphroditism,
sex, determined by nuclear chromatin, is
male, thus agreeing with the major aspects of
the phenotype. For female pseudohermaphroditism, individuals with adrenal hyperplasia or those without adrenal hyperplasia
give the female nuclear chromatin test. For
cases listed as true hermaphrodites Grumbach and Barr (1958) list 6 of the male type
and 19 of the female type. For the syndrome
of gonadal dysgenesis they list 90 as male
and 12 as female among the proved cases
and 15 more as female among those that are
56
BIOLOGIC BASIS OF SEX
suspected. In the syndrome of seminiferoustubule dysgenesis where there is tubular
fibrosis, 9 are listed as male and 18 female.
Where there is germinal aplasia, 15 are
listed as male and 1 as female. The seeming
difficulties in assigning a sex constitution
to some of these types are now being dissipated through the study of the full chromosome complements which are responsible
for these different disease conditions. As observations on different chromosome types
have been extended, evidence has accumulated to show that the numbers of sex nuclear
chromatins, for at least some of the nuclei
making up the organism, often equals
(n — 1) times the number of X chromosomes. The majority of male XY nuclei are
chromatin negative as are most of the Turner XO type. Female nuclei XX have a single chromatin positive element as do the
XXY and XXYY types. The XXX and
XXXY have 14 and 40 per cent respectively
with two Barr bodies in cases for which
quantitative data are available. However, a
child with 49 chromosomes, but whose cultured cell chromosomes appear as single
heteropycnotic masses making identification
of the individual chromosomes difficult,
showed 50 per cent of the cell nuclei with
three Barr elements (Fraccaro and Lindsten,
1960) . The chromosome constitution of these
nuclei was interpreted as trisomic for 8, 11,
and sex chromosomes. Sandberg, Crosswhite and Gordy (1960) report the case of a
woman 21 years old having various somatic
changes which does not fit this sequence. The
chromosome number was 47 and the nuclei
were considered trisomic for the sixth largest
chromosome. Two chromatin positive bodies
were ])rosent in the nuclei.
2. Chrotnosome Complement und Phenotijpe
in Man
Experience of the past 50 years has emphasized that genes and trisomies or other
types of aneuploid chromosome complexes
may lead to the development of abnormal
phenotypes expressing a variety of characteristics. Drosophila led the way in illustrating how the different gene or chromosome
arrangements may affect sex expression. Investigations of human abnormal types, particularly those with altered sex differentiation, have reccntlv .^liown that man follow.-^
other species in this regard. The Y carries
highly potent male influencing factors. Gene
differences often lead to characteristic phenotypes of unique form.
3. Testicular Feminization
The testicular feminization syndrome illustrates one of these types. As described by
Jacobs, Baikie, Court Brown, Forrest, Roy,
Stewart and Lennox (1959), "In complete
expression of this syndrome the external
genitalia are female, pubic and axillary hair
are absent or scanty, the habitus at puberty
is typically female, and there is primary
amenorrhoea. The testes can be found either
within the abdomen, or in the inguinal
canals, or in the labia majora, and as a rule
the vagina is incompletely developed. An
epididymis and vas deferens are commonly
present on both sides, and there may be a
rudimentary uterus and Fallopian tubes.
The condition is familial and is transmitted
through the maternal line." A sex-linked
recessive, a sex-limited dominant, and chromosome irregularities of the affected persons have been postulated as mechanisms
causing the apparent inheritance of this
condition. Chromosome examinations of the
cells of affected persons have shown 46 as
the total number and X and Y as the sex
complement. The karyotype analysis agrees
with the Barr nuclear chromatin test in
that the cells are chromatin-negative but
both are at variance with the sex phenotypes in the sense that aside from suppressed testes the patients are so completely
female. Genetically, Stewart (1959) has described two color-blind patients with the
testicular feminization syndrome in the first
five patients he reported. The limited data
from these cases suggest that the genie basis
for this condition is either independent or
but loosely linked with color blindness. This
evidence does not exclude sex-linkage but
does make it less probable. The third hypothesis of autosomal inheritance may take
one of several forms. A recessive gene which
affects only the male phenotypes when in
homozygous condition is apparently untenable because the matings from which
these individuals come are of the outbreeding type and the ratios apparently do not
differ from the one-to-one ratio expected of
a heterozygous dominant instead of that re
FOUNDATIONS FOR SEX
57
quired for an autosomal recessive. The hypothesis advanced by Witschi, Nelson and
Segal (1957), that the presence of an autosomal gene in the mother converts all her
male offspring into phenotypes of more or
less female constitution, in a manner comparable to that of the Ne gene in Drosophila (Gowen and Nelson, 1942) which
causes the elimination of all the female type
zygotes, is also made unlikely by the ratios
of normal to testicular feminization phenotypes observed in the progenies of these
affected mothers. The evidence favors a
simple autosomal dominant, acting only in
the male zygotes and perhaps balanced by
some genes of the X chromosome, which
have sufficient influence on the developing
male zygote to guide it toward an intermediate to nearly female phenotype. The
observations of Puck, Robinson and Tjio
( 1960) indicate that the action of a gene for
this condition may not be entirely absent
in the female, because in heterozygous condition in an XX individual it seemed to
delay menarche as much as 8 years. If this
delay be diagnostic for the heterozygote, it
will further assist in the genetic analysis of
this problem. Evidence on this point should
be a part of the genetic studies.
Cases closely similar to those described
by Jacobs, Baikie, Court Brown, Forrest,
Roy, Stewart and Lennox (1959) are
presented by Sternberg and Kloepfer
(1960). The patients show no trace of masculinity. They are remarkably uniform in
anatomic expression. Except for failure to
menstruate due to lack of uteri they undergo normal female puberty. Cryptorchid
testes, usually intra-abdominal, if removed
precipitate menopause symptoms. Four unrelated cases were found in this one study
with 7 additional cases traced through pedigree information. A total of 11 affected individuals was found in 6 sibships having
26 siblings of whom 5 were normal males.
In each kindred the inheritance was compatible with that of a sex-linkecl recessive
gene. A chromosomal study of a thyroid
tissue culture from one case revealed 46
chromosomes with normal XY male configuration. The individuals observed were
designated as simulant females."
4- Superfemale
The human superfemale has been recognized by Jacobs, Baikie, Court Brown, MacGregor, Maclean and Harnden (1959) in
a girl of medium height and weight, breasts
underdeveloped, genitalia infantile, vagina
small, and uterocervical canal 6 cm. in
length. Ovaries appeared postmenopausal
with normal stroma, and as indicated by a
biopsy specimen, deficient in follicle formation. Menstruation was thought to have
begun at age 14, but was irregular, occurring
every 3 to 4 months and lasting 3 days. The
last spontaneous menstruation was at 19.
Estrogen therapy caused some development
of the breasts and external genitalia, vagina,
and uterus with slight uterine bleeding. The
patient's parents were above 40 years of
age, mother 41, at time of her daughter's
birth.
Examination of sternal marrow cultures
showed 47 chromosomes in over 80 per cent
of the cells examined. The extra chromosome was the X, the chromosomal type
being XXX plus 22 pairs of autosomes.
Buccal smears showed 47 per cent of nuclei
contained a single chromatin body and 14
per cent contained 2 chromatin bodies as
expected of a multiple XX or XXX genotype. In comparison, 25 smears from 20 normal women had 36 to 51 per cent chromatin
positive cells but none of these contained
2 chromatin bodies. Two chromatin bodies
were seen in some cells of the ovarian stromal tissue. The patient showed a lack of
vigor, mentally was subnormal, was underdeveloped rather than overly developed in
the phenotypic sexual characteristics. Examination of the patient's mother showed
her to be XX plus 22 pairs of autosomes,
the normal 46 chromosomes.
Other cases show that types with XXX
plus 22 pairs of autosomes are of female
l)henotype but may vary in fertility and
development of the secondary sexual characteristics from nonfunctional to functional
females bearing children ( Stewart and Sanderson, 1960; Eraser, Campbell, MacGillivray, Boyd and Lennox, 1960). The triplo
X condition in man has a greater range of development and fertility than in Drosophila.
In man ovaries may develop spontaneously.
In Drosophila they require transplantation
58
BIOLOGIC BASIS OF SEX
to a diploid female host where they may attach to the oviducts and release eggs for
fertilization (Beadle and Ephrussi, 1937).
These cases present confirmation of two
facts already mentioned for Drosophila.
They show that when the X chromosome
has primarily sex determining genes, the
organism generally becomes unbalanced
when 3 of these X chromosomes are matched
against two sets of autosomes. The resulting phenotypes are female but relatively
undeveloped rather than overdeveloped.
The second is that the connotations evoked
by the prefix "super" are by no means applicable to this human type or to the Drosophila type.
The characteristics of the patient also
suggest that the autosomes may be carrying
sex genes opposing those of female tendencies as observed in both Drosophila and
Rumex genie imbalance.
5. Klinefelter Syndrome
In the Klinefelter syndrome there is male
differentiation of the reproductive tracts
with small firm descended testes. Meiotic or
mitotic divisions are rare, sperm are ordinarily not found in the semen. The type is
eunuchoid in appearance with gynecomastia, high-pitched voice, and sparse facial hair growth. Seminiferous tubules showing an increased number of interstitial cells
are atrophic and hyalinized. Urinary excretion of pituitary gonadotrophins is generally
increased, whereas the level of 17-ketosteroids may be decreased. The nuclear
chromatin is typically female. Of the dozen
or more cases studied (Jacobs and Strong,
1959; Ford, Jones, Miller, Mittwoch, Penrose, Ridler and Sha])iro, 1959; Bergman
and Reitalu quoted by Ford, 1960), only
one, having but 5 metaphase figures, had
less than 47 chromosomes in the somatic
cells and XXY sex chromosomes. That case
was thought to have typical female chromosomes XX + 22 AA. Two other cases were
of particular interest as indicating further
chromosome aberration. Ford, Jones, Miller,
Mittwoch, Penrose, Ridler and Shapiro
(1959) studied one patient who displayed
both the Klinefelter and Mongoloid syndromes. The chromosome number was 48,
the sex chromosomes being XXY and the
48tli chromosoinc being small acrocentric.
This individual had evidently developed
from an egg carrying 2 chromosomal aberrations, one for the sex chromosomes and the
second for one of the autosomes. The other
case, Bergman and Reitalu as cited by
Ford (1960), had 30 per cent of its cells
with an additional acrocentric chromosome
which had no close counterpart in the normal set.
Data where the Klinefelter syndrome occurs in families showing color blindness
(Polani, Bishop, Ferguson-Smith, Lennox,
Stewart and Prader, 1958; Nowakowski,
Lenz and Parada, 1959; and Stern, 1959a)
further test the XXY relationship and give
information on the possible position of the
color blindness locus with reference to the
kinetochore. Polani, Bishop, FergusonSmith, Lennox, Stewart and Prader (1958)
tested 72 sex chromatin-positive Klinefelter
patients for their color vision and found
that none was affected by red-green color
blindness. Nowakowski, Lenz and Parada
( 1959) tested 34 cases and detected 3 affected persons, 2 of whom were deuteranomalous and one protanopic. Stern (1959a)
l^oints out that these cases and their ratios
are compatible with the interpretation of
the Klinefelter syndrome as XXY. One of
the deuteranomalous cases had a deuteranomalous mother and a father with normal
color vision. This case could have originated
from a nondisjunctional egg carrying 2
maternal X chromosomes fertilized by a
sperm carrying a Y chromosome. The other
two cases had normal fathers with heterozygous mothers. There are several explanations by which the color-blind Klinefelter
progenies could be obtained. The heterozygotes might manifest the color-blind condition. The second hypothesis, which is
favored, is that of crossing over between the
kinetochore and the color-blind locus at the
first meiotic division to form eggs each
carrying 2 X chromosomes, one homozygous
for color blindness, and the other for normal
vision. An equational nondisjunction would
form eggs homozygous for color blindness
which on fertilization by the Y chromosomes of the male would give the necessary
XXY constitution for the color-blind male
which is Klinefelter in phenotype. A third
possibiHty is that these exceptions may
arise without crossing over as the result of
FOUNDATIONS FOR SEX
59
nondisjunction at the second meiotic division.
If the hypothesis of crossing over is accepted, the color-blind locus separates freely
from its kinetochore and would suggest that
the position of the locus is at some distance
from the kinetochore of the X chromosome.
A disturbed balance between the X and
the Y chromosomes alters the sexual type.
A single Y chromosome, contributing factors important to male development, is able
to alter the effects of two sets of female
influencing X chromosomes. Yet two Y
chromosomes in a complex of XXYY plus
44 autosomes seem to have little or no more
influence than one Y (Muldal and Ockey,
1960). The locations of the sex-influencing
genes in man are thus more like those of the
plant Melandrium than of Drosophila in
which the male-determining factors occur
in the autosomes. The relative potencies of
the male sex factors compared with those of
the female, however, are much less than
those in Melandrium.
6. Turner Syndrome
Turner's syndrome or ovarian agenesis
further substantiates the female influence
of the X chromosomes. The cases occur as
the developmental expression of accidents in
the meiotic or mitotic divisions of the chromosomes. These accidents lead to adults
unbalanced for the female tendencies of the
X chromosome. The gonads consist of connective tissue. The rest of the reproductive
tract is female. Growth stimuli of puberty
are lacking, resulting in greatly reduced female secondary sexual development. Patients are noticeably short and may be abnormal in bone growth. In its more extreme
form, designated as Turner's syndrome, the
individuals may show skin folds over the
neck, congenital heart disease, and subnormal intellect, as well as other metabolic
conditions. Earlier work (Barr, 1959; Ford,
Jones, Polani, de Almeida and Briggs,
1959) shows that 80 per cent of the nuclear chromatin patterns are of the male
type. Evidence from families having both
this condition and color blindness suggested
that at least some of the Turner cases would
be found to have 45 chromosomes, the sex
chromosome being a lone X (Polani, Lessof
and Bishop, 1956). Work of Ford, Jones,
Polani, de Almeida and Briggs, (1959)
has confirmed this hypothesis and added the
fact that some of these individuals are also
mosaics of cells having 45 and 46 chromosomes. The 45 chromosome cells had but one
X, whereas the 46 had two X's. This finding
may explain the female-chromatin cell type
observed in about 20 per cent of the cases
having the Turner syndrome. Such mosaics
of different chromosome cell types could
also be significant in reducing the severity
of the Turner syndrome and in increasing
the range of symptoms which characterize
this chromosome-caused disease as contrasted with those characterizing Turner's
disease. Further cases observed in other
investigations, Fraccaro, Kaijser and Lindsten (1959), Tjio, Puck and Robinson
(1959), Harnden, and Jacobs and Stewart
cited by Ford (1960) have all shown 45
chromosome cells and a single X chromosome. As with the XXX plus 44 autosome
super females, the Turner type, X plus 44
autosomes, also shows a rather wide range
in development from sterility with extensive
detrimental secondary effects to nearly normal in all respects. Bahner, Schwarz, Harnden, Jacobs, Hienz and Walter (1960) report a case which gave birth to a normal
boy. Other cases have been described (Hoffenberg, Jackson and jVIuller, 1957; Stewart,
19601 in which menstruation was established over a period of years. The XO type
in man and Melandrium is morphologically
female. In Drosophila on the other hand,
the XO type is phenotypically nearly a
perfect male. It is further to be noted that
the X chromosome of Drosophila appears to
have a less pronounced female bias than
that of man when balanced against its associated autosomes, inasmuch as the XO +
2A type in Drosophila is male as contrasted
with the XO + 2A type in man which is
female. At the same time it seems that the
autosomes in the human may be influential
in that the female gonadal development is
suppressed instead of going to completion
as it does in the XX type.
7. Hermaphrodites
Hermaphroditic phenotypes in man, to
the number of at least 74 (Overzier, 1955),
have been observed and recorded since
1900. Types with a urogenital sinus pre
60
BIOLOGIC BASIS OF SEX
dominated. The uteri were absent in some
cases, even when complete external female
genitalia were present. Ovotestes were found
on the right side of the body in over half
the cases; separate left ovaries or testes
were about equally frequent ; in three cases
separate testis and ovary were indicated.
The left side of the body showed a different
distribution of gonad types; about onefourth had ovotestes, another fourth ovaries, and one-twelfth testes. Unilateral distribution of gonad types was most frequent.
The presence or absence of the prostate
seemed to have significance because it is
sometimes absent in purely female types. In
recent literature similar cases have been
called true hermaphrodites. This is an exaggeration in terms of long established
practice in plants and animals where true
hermaphroditism includes fully functioning
gametes of each sex.
Hungerford, Donnelly, Nowell and Beck
(1959» have reported on a case of a Negro
in which the culture cells had the chromosome complement of a normal female 46,
with XX sex chromosomes. Unfortunately,
the possibility that this case may be a chromosome mosaic was not tested by karyotype samples from several parts of the body.
Harnden and Armstrong (1959) established separate skin cultures from both sides
of the body of another hermaphroditic type.
The majority of the cells were apparently of
XX constitution with a total of 46 chromosomes. However, in one of the 4 cultures
established, some 7 per cent of cells had an
abnormal chromosome present, suggesting
that the case might involve a reciprocal
translocation between chromosomes 3 and
4 when the chromosomes were ordered according to size. All the other cell nuclei were
normal. The fact that the majority of the
cells in these two cases were XX and with
46 chromosomes seems to predicate against
the view that either changes in chromosome
number or structure of the fertilized egg are
necessary for the initiation of hermaplu'odites.
Ferguson-Smith (1960) describes two
cases of gynandromorphic type in which the
reproductive organs on the left side were
female and on the right side were male. The
recognizable organs were Fallopian tube,
ovary with primordial follicles only, imma
ture uterus in one case, none in the other,
rudimentary prostate, small testis and epididymis, vas deferens, bifid scrotum, phallus, perineal urethra, pubic and axillary
hair, breasts enlarging at 14 years. Testicular development with hyperplasia of Leydig
cells, germinal aplasia, and hyalinization of
the tubules was suggestive of the Klinefelter
syndrome. Nuclear-chromatin was positive
in both cases. Modal chromosome number
was 46. The sex chromosomes were interpreted as XX. The 119 cell counts on one
patient showed a rather wide range; 7 per
cent had 44 chromosomes, 13 per cent had
45, 62 per cent had 46, and 18 per cent had
47 chromosomes. The extra chromosome
within the cells containing 47 chromosomes
was of medium size with submedian kinetochore as generally observed for chromosomes of group 3.
It is surprising that the male differentiation in these four and other hermaphroditic
cases (Table 1.5) is as complete as it is.
Other observations show that the Y chromosome contains factors of strong male
potency, yet in its absence the hermaphrodites develop an easily recognized male
system. It is not complete but the degree of
gonadal differentiation is as great as that
observed in the XXY 4- 2A Klinefelter
types. The bilateral sex differentiation in
hermaphrodites would seem to require other
conditions than those heretofore considered.
Another case of hermaphroditism is that
presented by Hirschhorn, Decker and
Cooper (1960). The patient's j:)henotype
was intersexual with phallus, hypospadias,
vagina, uterus. Fallopian tubes, two slightly
differentiated gonads in the position of ovaries. The child was 4 months old. Culture
of bone marrow cells showed that the individual was a mosaic of two types. About
60 per cent of the cells had 45 chromosomes
of XO karyotype, and 40 per cent had 46
chromosomes with a karyotA'^pe XY. The
Y chromosome when present was larger
than Y chromosomes of normal individuals.
The change in size may be related to the
association of the XO and XY cells and
be similar etiologically to the case discussed
by yivtz (1959) in Sciara triploids.
There are mosaics in Drosophila formed
from the loss by the female in some cells of
one of lioi- X chromosomes, as for instance
FOUNDATIONS FOR SEX
61
in ring chromosome types, which may display primary and secondary hermaphroditic
development. For this to happen the altered
nuclei apparently find their way into the
region of the egg cytoplasm which is to
differentiate into the reproductive tract. As
seen in the adults, organ tissue of one chromosome type is cell for cell sharply differentiated from that of the other chromosome
type with regard to sex. These observations
indicate that for these mosaics the basic
chromosome structure of the cell itself
determines its development. In fact most
mosaics of this species show this cell-restricted differentiation. Several problems
arise when these well tested observations
are considered in comparison with those
now arising in the chromosome mosaics of
the sex types in man. It would seem unlikely
that the bone marrow cells or for that
matter any somatic cells not a part of the
reproductive tract would operate to modify
the adult sex or a part thereof. Rather the
developmental secjuence should start from
cell differences within the early developing
reproductive tract. Circulatory cells or substances would be of dubious direct significance from another viewpoint. All cells of
the body would ultimately be about equally
affected by any cells or elements circulating
in the blood. With strong male elements
and strong female elements the result expected would be a reduction in sex development of either sex instead of the sharply
differentiated organ systems which are observed. This raises the question, are the
chromosomally differentiated cell sex mosaics primary to or secondarily derived
from the tissues of the ultimate hermaphrodites? Study of the cell structure of the sex
organs themselves as well as much other
information will be necessary to clear up
this problem.
There are, however, other types of controlled sex development, as by various
genes, which lead to the presence of both
male and female sexual systems. Genes
for these phenotypes are relatively rare, but
once found are transmitted as commonly
expected. The inherited hermaphroditic
cases in Drosophila are certainly relevant
to the testicular feminization syndrome in
man. Are they equally pertinent to the
highly sporadic hermaphroditic forms just
considered for man? If so, they indicate a
genie basis for these types which would
probably be beyond the range of the microscope to detect. The low frequency of true
hermaphrodites in the human, together with
lack of information on possible inheritance
mitigates against the genie explanation ; although genie predisposition acting in conjunction with rare environmental events as
occurs in our Balb/Gw mice (Hollander,
Go wen and Stadler, 1956 ) could explain the
rare hermaphrodites observed in that particular line of mice and a limited number of
its descendants.
8. XX XY + U Autosome Type
The XXXY -I- 44 autosome type in the
human has been studied by Ferguson-Smith,
Johnson and Handmaker (1960) and
Ferguson-Smith, Johnston and Weinberg
(1960). The two cases described were characterized by primary amentia, microorchidism and by two sex chromatin bodies
in intermitotic nuclei. The patients were
similar in having disproportionately long
legs; facial, axillary, and abdominal hair
scant; pubic hair present; penes and scrota
medium to well developed ; small testes and
prostates; vasa deferentia and epididymides
normally developed on both sides of the
body and no abnormally developed Miillerian derivatives. Testes findings were like
those in Klinefelter cases with chromatinpositive nuclei, small testes with nearly
complete atrophy, and hyalinization of
seminiferous tubules and islands of abnormal and pigmented Leydig cells in the
hyalinized areas. The few seminiferous
tubules present were lined with Sertoli cells
but were without germinal cells. Nuclear
chromatin was of female type. About twofifths of the nuclei had double and twofifths single sex chromatin. The modal chromosome count for bone marrow cells was
48, 75 per cent of the cells having this
number. Chromosome counts spread from
45 to 49. This type, XXXY plus 44 autosomes, may be looked upon as a superfemale
plus a Y or a Klinefelter plus an X chromosome. In either case the male potency of
the genes in the Y chromosome is able to
dominate the female tendencies of XXX to
develop nearly complete male phenotypes.
Both cases had severe mental defects but
TABLE 1.5
Chromosome kinds and numbers for different recognized sex types in man
External
Type
Male
Female
Female (rare hemophilic)
Eunuchoid female
Female
Female
Female
Female
Female
Female
Male .
Male.
Male.
Male.
Male.
Male . . .
Female.
Female .
Female .
Female .
Male.
Male.
Hermaphrodite
Hermaphrodite.
Intersex
Numbers of
Chromosomes
chromosoil rearrange
1 + X
fragment
1
2
2
2
2
Interpreted a.s
XX trisomic
for Sand 11 or
as XXXX
4X + Yl
3X+ Yj
1
3
3
2l
/mosaic
Missing
or Extra
Chromosomes
? Chr
mosome 3
orT(X;A)
Small
autosome
? Large
chromosome or
T(X;A)
X or Y
(X or Y)
+21
46,47,48
cliromosomes
X, Y
X or Y
-fA set
Sex Chromatm
Negative
Positive
Negative
Negative
Positive
Negative
Positive
Negative
Negative
Negative
Negative
Negative ±
Negative
Positive
Positive
Triple positi
Negative
Double posit
Double posit
Negative
Double posit
Negative
Negative
Negative
Designating Term
Normal male
Normal female
Pure gonadal dysgenesis
CJonadal dysgenesis
Testicular feiuinizati
Turner
Turner type female
Tinner? gave birth to boy
Turner
Turner
Klinefelter
Klinefelter mongoloid
Klinefelter
Klinefelter
Klinefelter
Klinefelter
Sujierfemale
Superfemale gave birtli to
children
Testicular deficiency
Precocious puberty
Triploid
Hermaphrodite or intersex dei)cnding on definition
Investigators*
2
3, 4, 5,
5, 12, 13, 14, 40, 41
41
16, 17, 18, 40, 41
19
40
23, 40
24, 25
41
26
29, 30, 31,. 32, 33
35, 39, 40
34
41
Tjio and Levan, 1956.
Nilsson, Bergman, Reitalu and Waldenstrom, 1959.
Harnden and Stewart, 1959.
Stewart, 1960b.
Stewart, 1960a.
Elliott, Sandler and Rabinowitz, 1959.
Jacobs, Baikie, Court Brown, Forrest, Roy, Stewart and Lennox, 1959.
Stewart, 1959
Lubs, Vilar and Bergenstal, 1959.
Sternberg and Kloepfer, 1960.
Puck, Robinson and Tjio, 1960.
Ford, Jones, Polani, de Almeida and Briggs, 1959.
Fraccaro, Kaijser and Lindsten, 1959.
Fraccaro, Kaijser and Lindsten, 1960a.
15. Bahner, Schwarz, Harnden, Jacobs, Hienz and Walter, 1960.
16. Jacobs and Strong, 1959.
17. Bergman, Reitalu, Nowakowski and Lenz, 1960.
18. Nelson, Ferrari and Bottura, 1960.
19. Ford, Jones, Miller, Mittwoch, Penrose, Hidlor and Shapiro,
1959.
20. Ford, Polani, Briggs and Bishor), 1959.
21. Crooke and Hayward, 1960.
22. Muldal and Ockey, 1960.
23. Jacobs, Baikie, Court Broun, MacCJregor, Maclean and
Harnden, 1959.
24. Eraser, Campbell, .MacCiillivray, Boyd and Lennox, 1960.
25. Stewart and Sanderson, 1960.
26. Jacobs, Harnden, Court Brown, Cohl.stein, Close, Mac
Gregor, Maclean and Strong, 1960.
62
FOUNDATIONS FOR SEX
63
27. Ferguson-Smith, Johnston and Handiiiaker, 196(
28. Book and Santesson, 1960.
29. Harnden and Armstrong, 1959.
30. Hungerford, Donnelly, Nowell and Beck, 1959.
31. Ferguson-Smith, Johnston and Weinberg, 1960.
32. deAssis, Epps, Bottura and Ferrari, 1960.
33. Gordon, O'Gorman, Dewhurst and Blank, 1960
34. Hirschhorn, Decker and Cooper, 1960.
35. Sasaki and Makino, 1960.
36. Bloise, Bottura, deAssis, and Ferrari, 1960,
37. Fraccaro, Kaijser and Lindsten, 1960c.
37a. Fraccaro and Lindsten, 1960.
38. Fraccaro, Ikkos, Lindsten, Luft and Kaijser, 1960.
39. Harnden, 1960.
40. Ferguson-Smith and Johnston, 1960.
41. Sandberg, Koepf, Crosswhite and Hauschka, 1960.
42. Hayward, 1960.
it should be remembered that they were
sought in institutions for which this is a
criterion of admittance. Their mental ability was distinctly less than that of Klinefelter XXY cases which have come under
study. The pattern of the XXXY effects on
the reproductive tract, however, was comparable with that observed in the XXY
genotypes. The effects of one Y chromosome
were balanced by either two or three X
chromosomes to give nearly equal phenotypic effects.
9. XXY + 66 Autosome Type
XXY + 66 autosome type was established by Book and Santesson (1960) for
an infant boy having several somatic anomalies which may or may not be relevant to
the sex type. Externally the genitalia were
normal for a male of his age, penis and
scrotum with testes present in the scrotum.
Again the Y chromosome demonstrates its
male potencies over two X's even in the
presence of three sets of autosomes. The
case is of particular significance since further development may indicate what male
potencies an extra set of autosomes may
possess.
10. Summary of Types
Other types of sex modifying chromosomal combinations and their contained
genes have been observed particularly as
mosaics or as chromosomal fragments added
or substracted from the normal genomes.
No doubt other types will be discovered
during the mushroom growth of this period.
Time can only test the soundness of the
observations for the field of human chromosomal genetics and cytology is difficult
at best requiring special aptitudes and experience. Mistakes, no doubt, will be made.
The status of the subject is summarized
in Table 1.5.
11. Types Unrelated to Sex
Other cases not related to sex or only
secondarily so were scrutinized during the
course of these studies. The information
gained from them is valuable as it strengthens our respect for the mechanisms involved. The sex types which are dependent
on loss or gain of the X and/or Y chromosomes belong to the larger category of
monosomies or trisomies. Numbers of autosomal monosomic and trisomic syndromes
have also been identified in the course of
these investigations. Similarly, not all cases
that have been studied have turned out to
be associated with chromosomal changes.
This in itself is important since it lends
confidence in those that have, as well as
redirects research effort toward the search
for other causes than chromosomal misbehavior. The first trisomic in man was
identified through the study of Mongolism.
The condition affects a number of primary
characteristics but not those of sex, for
males and females occur in about equal
numbers. The broad spectrum of these effects points to a loss of balance for an
equally extensive group of genes in the two
sexes. The common association of characteristics making up these Mongoloids, together with their sporadic appearance and
their change in frequency with maternal
age, all suggest the findings which Lejeune,
Gautier and Turpin (1959a, b) and Lejeune,
Turi)in and Gautier (1959a, b) were able
to demonstrate so successfully. They established that the tissue culture cells of Mongoloid imbeciles had 47 chromosomes and that
the extra chromosome was in the small
acrocentric group. Lejeune, Gautier and
Turpin (1959a, b) have now confirmed
these observations on not less than nine
cases. Jacobs, Baikie, Court Brown and
Strong (1959), Book, Fraccaro and Lindsten (1959) and Fraccaro (cited by Ford,
1960) as well as later observers have substantiated the results on more than ten
other cases. The well known maternal age
effect, whereby women over 40 have a
chance of having IMongoloid offspring 10
to 40 times as frequently as those of the
younger ages, would seem to point to non
64
BIOLOGIC BASIS OF SEX
disjunction in oogenesis as the most important cause of this condition. Some women
who have had previous JMongoloid progeny
have an increased risk of having others.
This is an important consideration in that
genetic factors may materially assist in
bringing about nondisjunction in man as
they are known to do in Drosophila (Gowen
and Gowen, 1922; Gowen, 1928). The products of the nondisjunctions approach those
expected on random distribution of the
chromosomes (Gowen, 1933) so that occasionally more than one type of chromosome
disjunction will appear in a given individual. Such a case is that illustrated by
Ford, Jones, Miller, Mittwoch, Penrose,
R idler and Shapiro (1959) in which the
nondisjunctional type included not only
that for the chromosome important to Mongolism but also the sex chromosomes significant in determining the Klinefelter
condition. This individual showed 48 chromosomes, 22 pairs of normal autosomes, 3
sex chromosomes XXY, and a small acrocentric chromosome matching a pair of
chromosomes, the 21st, within the smallest
chromosomes of the human idiogram. The
analysis of Mongolism showed the way for
the separation of the various human sex
types through chromosome analyses.
Chromosome translocations furnish another means of establishing an anomaly
that may then continue on an hereditary
basis as either the male or female may
transmit the rearranged chromosomes. Polani, Briggs, Ford, Clarke and Berg (1960),
Fraccaro, Kaijser and Lindsten (1960b),
Penrose, Ellis and Delhanty (1960) and
Carter, Hamerton, Polani, Gunalp and
Weller (1960) have studied Mongoloid
cases which they interpreted in this manner.
In some cases the rearranged chromosomes
have been transmitted for three generations.
Several of the translocations were considered to include chromosomes 15 and 21.
Another trisomic autosomal type was rc])ortcd by Patau, Smith, Therman, Inhorn
and Wagner (1960). The patient was female and had 47 chromosomes. The extra
chromosome was a medium-sized acrocentric autosome belonging to the D group.
Despite extensive malformations affecting
several organs the patient lived more than
a year. Another female iiortraying the same
syndrome has since been found, so other
cases may be expected. Among the characteristics are mental retardation, minor motor seizures, deafness, apparent micro or
anophthalmia, horizontal palmar creases,
trigger thumbs, Polydactyly, cleft i)alate,
and hemangiomata.
The third trisomic type was also reported
by Patau, Smith, Therman, Inhorn and
Wagner (1960). Six individuals have been
observed. The characters affected are mental retardation, hypertonicity (5 patients),
small mandible, malformed ears, flexion of
fingers, index finger overlaps third, big toe
dorsiflexed (at least 4), hernia and/or diaphragm eventration, heart anomaly (at
least 4), and renal anomaly (3). The sexes
were two males and four females. The extra chromosome was in the E group and was
diagnosed as number 18. Edwards, Harnden,
Cameron, Crosse and Wolff (1960) have
described a similar case but they consider
the trisomic to be number 17. Ultimate comparisons of these types no doubt will decide
if this is a 4th trisomic or if all the cases
belong in the same group.
The Sturge-Weber syndrome apparently
is caused by another trisomic. Locomotor
and mental abilities are retarded. Hayward
and Bower (1960) interpret the 3 chromosomes responsible as the smallest autosomes,
number 22, of the human group.
Trisomic frequencies should be matched
by equal numbers of monosomies. Turpin,
Lejeune, Lafourcade and Gautier (1959)
have reported polydysspondylism in a child
with low intelligence, dwarfing, and multil)le malformations of spine and sella turcica.
The somatic cell chromosome count was
only 45 but one of the smallest acrocentric
chromosomes appeared to have been translocated, the greatest part of this chromosome being observed on the short arm of one
of the 3 longer acrocentric chromosomes.
Th(> condition appears to be unique and not
likely to be found in other unrelated famiVws. However, the phenotyj^ic effects were
so severe that all members of the proband's
family would seemingly be worthy of careful sur\'('y for their chromosome characteristics.
The comi)lex pattern of multiple anomalies renders each syndrome distinct from
the othei's. Chromosome losses or gains from
FOUNDATIONS FOR SEX
Go
the normal diploid would be expected to
lead to the complex changes. Mongolism is
influenced by age of the mother and probably to some extent by her inheritance. It
is to be expected that the other trisomies
may show parallel relations. Other trisomies
may be expected although, as the chromosomes increase in size, a group of them will
have less opportunity to survive because of
loss of balance with the rest of the diploid
set. Thus far most of these conditions affect the sex phenotypes. This is in accord
with the results in Drosophila. Changes in
the balance of the X chromosomes are less
often lethal than the gain or loss of an autosome. Other animals show like effects. In
plants, loss or gain of a chromosome, although generally detrimental, often causes
less severe restrictions on life. Harmful effects are observed but do not cause early
deaths. This may be because many aneuploids are within what are presumably
polyploid plant species.
Ford (1960) has collected the data on 13
different phenotypes that could come under
suspicion of chromosomal etiology as examined by a number of workers. Careful
cytologic examination of patients suffering
from one or another of these diseases has
shown that the idiograms were normal in
both number and structure of the chromosomes. The disease conditions were:
acrocephalosyndactyly, arachnodactyly
(Marfan's syndrome), chondrodystrophy,
Crouzon's disease, epiloia, gargoylism, Gaucher's disease, hypopituitary dwarfism,
juvenile amaurotic idiocy, Laurence-MoonBiedl syndrome. Little's disease, osteogenesis imperfecta, phenylketonuria, and anencephalic types. To this list Sandberg, Koepf ,
Crosswhite and Hauschka (1960) have now
been added neurofibromatosis, Lowe's syndrome, and pseudohypoparathyroidism.
F. SEX RATIO IN MAN
Sex ratio studies on human and other animal populations have always been large in
volume. The period since 1938 is no exception. Geissler's (1889) data on family sex
ratios, containing more than four million
births, have been reviewed and questions
raised by several later analysts. Edwards
(1958) has reanalyzed the clata from this
population and considered these points and
reviewed the problems in the light of the
following questions: (1) Does the sex ratio
vary between families of the same size? (2)
Do parents capable of producing only unisexual families exist? (3) Can the residual
deviations in the data be satisfactorily explained? Probability analyses were based
on Skellam's modified binomial distribution,
a special case of the hypergeometrical. The
following conclusions were drawn. The
probability of a birth being male varies
between families of the same size among
a complete cross-section of this 19th century
German population. There is no evidence
for the existence of parents capable of producing only unisexual families. With the
assumption that proportions of males vary
within families, the apparent anomalies in
the data appear to be explicable. These
studies have a bearing on the variances observed in further work dealing with family
differences such as that of Cohen and Glass
( 1959) on the relation of ABO blood groups
to the sex ratio and that of Novitski and
Kimball (1958) on birth order, parental age,
and sex of offspring. Novitski and Kimball's data are of basic significance, for the
interpretations are based on a large volume
of material covering a one-year period in
which improved statistical techniques were
utilized in the data collection, in showing
that within these data sex ratio variation
showed relatively little dependence on age
of mother, whereas it did show dependence
on age of father, birth order, and interactions between them. These observations
have direct bearing on the larger geographic
differences observed in sex ratios as discussed by Russell (1936) and have recently
been brought to the fore through the studies
of Kang and Cho (1959a, b). If these data
stand the tests for biases, they are of significance in showing Korea to have one of the
highest secondary sex ratios of any region,
113.5 males to 100 females, as contrasted
with the American ratio of about 106 males
to 100 females. Of similar interest is the
lower rate of twin births, 0.7 per cent in
Korea vs. about 1 per cent in Caucasian
populations and the fact that nearly twothirds of these tW'in births in Korean peoples
are identical, whereas those in the Caucasian groups are only about half that number. The reasons for these differences must
66
BIOLOGIC BASIS OF SEX
lie in the relations of the human X and Y
chromosomes and autosomes and the balance of their contained genes. Little or
nothing is known about how these factors
operate in the given situations.
Acknowledgment. In formulating and
organizing the material on which this paper
is based I have been fortunate in the helpful
discussions and analytical advice contributed so generously by Doctors H. L. Cai'son,
K. W. Cooper, H. V. Grouse, C. W. Metz,
S. B. Pipkin, W. C. Rothenbuhler, and H. D.
Stalker, and others having primary research
interests in this field. To them, and particularly to my research associates Doctors S.
T. C. Fung and Janice Stadler, our secretary Gladys M. Dicke and to my wife,
]\Iarie S. Gowen, I tender grateful acknowledgment for their contributions to the manuscript. Direct reference is made to some 300
investigations in the body of the paper but
the actual number, many of which could
equally well have been incorporated, that
furnished background to these advances is
much larger, more than 1600. To this vast
effort toward understanding the foundations
for sex we are all indebted.
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