Book - Aids to Embryology (1948) 14: Difference between revisions

From Embryology
mNo edit summary
Line 1: Line 1:
{{Baxter1948 header}}
{{Baxter1948 header}}
==Chapter XIV  The Transmission Of Hereditary Characters==
=Chapter XIV  The Transmission of Hereditary Characters=


Every potential individual, that is, every fertilised  
Every potential individual, that is, every fertilised ovum, commences development with a complement of hereditary factors (genes) derived from both parents at the time of union of the germ cells in fertilisation. These inherited factors operate during development, both before and after birth, to produce an individual resembling the parents. The environment, both prenatal and post-natal, may influence some of these hereditary characters and modify them, but there are certain characters which cannot be affected by the environment and hence are said to be determined at fertilisation. Examples of these are the blood group to which the person belongs and the colour of the eyes. The study of these hereditary factors, and the laws which govern their transmission from parents to offspring, is known as the science of genetics.
ovum, commences development with a complement  
of hereditary factors (genes) derived from both parents  
at the time of union of the germ cells in fertilisation.  
These inherited factors operate during development,  
both before and after birth, to produce an individual  
resembling the parents. The environment, both prenatal and post-natal, may influence some of these  
hereditary characters and modify them, but there are  
certain characters which cannot be affected by the  
environment and hence are said to be determined  
at fertilisation. Examples of these are the blood  
group to which the person belongs and the colour of  
the eyes. The study of these hereditary factors, and  
the laws which govern their transmission from parents  
to offspring, is known as the science of genetics.  




HEREDITARY CHARACTERS 169  
HEREDITARY CHARACTERS 169




Genetic laws are fundamentally the same for plants  
Genetic laws are fundamentally the same for plants and animals, and since many generations of plants and lower animals can be investigated in a relatively short period of time, the study of genetics has largely been based on them. In addition, certain forms possess chromosomes particularly favourable to the genetic analysis of experimental procedures. But in all cases where genetic laws have been tested in lower forms they have been found applicable to human hereditary.
and animals, and since many generations of plants and  
lower animals can be investigated in a relatively  
short period of time, the study of genetics has largely  
been based on them. In addition, certain forms  
possess chromosomes particularly favourable to the  
genetic analysis of experimental procedures. But  
in all cases where genetic laws have been tested in  
lower forms they have been found applicable to  
human hereditary.  




Parent ^ Tfc\l (T) "H Dw&rf (d)  
Parent ^ Tfc\l (T) "H Dw&rf (d)


fj. AU hybrid Tidls (Td)  
fj. AU hybrid Tidls (Td)


1 ^ l
1 ^ l




Td  
Td




Td  
Td




Hybrid Tidls  
Hybrid Tidls




dd  
dd


Pure Dvj&rfs  
Pure Dvj&rfs




1 1 1 r  
1 1 1 r


Td Td dd TT  
Td Td dd TT




1  
1




i  
i




d Td dd  
d Td dd




k dd  
k dd All Pure Ow^ris
All Pure  
Ow^ris  




y IG< 42 . — Schematic Table showing Mendelian Inheritance AS APPLIED TO TALL AND DWARF PEAS.  
y IG< 42 . — Schematic Table showing Mendelian Inheritance AS APPLIED TO TALL AND DWARF PEAS.


T = tall ; d = dwarf.  
T = tall ; d = dwarf.




The fundamental genetic laws are based on the  
The fundamental genetic laws are based on the experiments of Mendel (1866) on garden peas. Mendel studied the inheritance of a number of characters of this form, of which tallness and dwarfness may be taken as a typical example. If a tall pea and a dwarf pea were cross-fertilised and the resultant peas planted, all of the plants that grew from them were tall. These he called the first filial generation (Fj). These tall cross-bred plants were allowed to produce peas by self-fertilisation, and when such were sown the second filial generation (F a ) showed some plants that were tall and some that were dwarf,
experiments of Mendel (1866) on garden peas. Mendel  
studied the inheritance of a number of characters of  
this form, of which tallness and dwarfness may be  
taken as a typical example. If a tall pea and a  
dwarf pea were cross-fertilised and the resultant  
peas planted, all of the plants that grew from them  
were tall. These he called the first filial generation  
(Fj). These tall cross-bred plants were allowed to  
produce peas by self-fertilisation, and when such  
were sown the second filial generation (F a ) showed  
some plants that were tall and some that were dwarf,  




AIDS TO EMBRYOLOGY  
AIDS TO EMBRYOLOGY




170  
170


in the proportion of three tall to one dwarf. Peas  
in the proportion of three tall to one dwarf. Peas derived from self-fertilisation of each of the dwarf plants were then sown, and they produced dwarf plants only ; seed from some of the self -fertilised tall plants produced both tall and dwarf offspring, in the proportion of three tall to one dwarf ; the remainder of the seed from the tall plants produced nothing but tall offspring in the third (F s ) generation (see Fig. 42 for details).
derived from self-fertilisation of each of the dwarf  
plants were then sown, and they produced dwarf  
plants only ; seed from some of the self -fertilised  
tall plants produced both tall and dwarf offspring,  
in the proportion of three tall to one dwarf ; the  
remainder of the seed from the tall plants produced  
nothing but tall offspring in the third (F s ) generation  
(see Fig. 42 for details).  


From these experiments it is clear that an attempt  
From these experiments it is clear that an attempt was being made by nature to separate the original pure characters of tallness and dwarfness in the
was being made by nature to separate the original  
pure characters of tallness and dwarfness in the  




Parents  
Parents


— Y  
— Y


+ dd  
+ dd


4  
4


P&rent G&mefes  
P&rent G&mefes


T  
T


»  
»


d  
d


j 1  
j 1


F 1  
F 1




.Td  
.Td


Fj. Q&metes  
Fj. Q&metes


_T.  
_T.


d. T. d.  
d. T. d.




F t T ~ v7~ 1 ' >  
F t T ~ v7~ 1 ' >


F * TT. Td. Td. dd.  
F * TT. Td. Td. dd.


Fig. 43. — Schematic Table to show Segregation of the  
Fig. 43. — Schematic Table to show Segregation of the Tall and Dwarf Genes in the Gametes of Peas.
Tall and Dwarf Genes in the Gametes of Peas.  


T = tall ; d = dwarf.  
T = tall ; d = dwarf.


parent stock from the hybrids. This is known as the  
parent stock from the hybrids. This is known as the law of segregation. The character of tallness, which was found in the F x generation, is known as a dominant character since it overshadows the recessive character of dwarfness. These characters are known to be caused by certain elements on the maternal and paternal chromosomes called genes.
law of segregation. The character of tallness, which  
was found in the F x generation, is known as a dominant  
character since it overshadows the recessive character  
of dwarfness. These characters are known to be  
caused by certain elements on the maternal and  
paternal chromosomes called genes.  


Consideration of Fig. 43 will indicate how these  
Consideration of Fig. 43 will indicate how these dominant and recessive factors become separated out during breeding. The parent stock possessed either the character of tallness or dwarfness in pure form, that is, when self -fertilised they always bred true. The first filial generation (Fj) were all tall since the
dominant and recessive factors become separated out  
during breeding. The parent stock possessed either  
the character of tallness or dwarfness in pure form,  
that is, when self -fertilised they always bred true.  
The first filial generation (Fj) were all tall since the  




HEREDITARY CHARACTERS 171  
HEREDITARY CHARACTERS 171


gene for dwarfness was present but masked by the  
gene for dwarfness was present but masked by the dominant tall (T) gene. The gametes (sex cells) of the Fj generation contained the genes for tallness and dwarfness in equal numbers so that when such plants were self-fertilised the dominant T gene would be present in three out of four of the offspring and they would all be tall plants. In one out of the four, two d (dwarfness) genes would be present and hence these plants would be dwarfs, and on further selffertilisation would continue to breed truly dwarf. One of the three tall plants would contain only genes for tallness and so on self-fertilisation it would continue to breed true for the character of tallness. The remaining two tall plants contained Td genes, and further inbreeding of them would result in the formation of dominant and recessive forms in the ratio of three dominant to one recessive.
dominant tall (T) gene. The gametes (sex cells) of  
the Fj generation contained the genes for tallness and  
dwarfness in equal numbers so that when such  
plants were self-fertilised the dominant T gene would  
be present in three out of four of the offspring and  
they would all be tall plants. In one out of the four,  
two d (dwarfness) genes would be present and hence  
these plants would be dwarfs, and on further selffertilisation would continue to breed truly dwarf.  
One of the three tall plants would contain only  
genes for tallness and so on self-fertilisation it would  
continue to breed true for the character of tallness.  
The remaining two tall plants contained Td genes,  
and further inbreeding of them would result in the  
formation of dominant and recessive forms in the  
ratio of three dominant to one recessive.  


In human genetics there are certain clear-cut  
In human genetics there are certain clear-cut cases of inheritance due to dominant factors. Examples of these are congenital brachydactyly, syndactyly, and congenital night blindness. Also black hair colour is dominant over brown hair colour, and so is brown iris colour over blue.
cases of inheritance due to dominant factors. Examples of these are congenital brachydactyly, syndactyly, and congenital night blindness. Also black  
hair colour is dominant over brown hair colour, and  
so is brown iris colour over blue.  


Mendelian laws have been applied to animals and  
Mendelian laws have been applied to animals and they have been found to hold equally good for them. For example, the colour of the ordinary brownishgrey wild mouse is due to bands of pigment in its hair ; black at the base and yellow at the tip. This is known as “ agouti ” colouration. But in fancy mice there is a variety in which the hair appears black, due to the absence of the yellow tip to the hair. If a pure agouti mouse is crossed with a black or non-agouti, the offspring at Fj are all agouti in colour — that is, the agouti factor is dominant over the non-agouti, which is the recessive factor. If however these hybrids are inbred, the F 2 generation comes out as 25 per cent, pure agouti, 50 per cent.
they have been found to hold equally good for them.  
For example, the colour of the ordinary brownishgrey wild mouse is due to bands of pigment in its  
hair ; black at the base and yellow at the tip. This  
is known as “ agouti ” colouration. But in fancy  
mice there is a variety in which the hair appears  
black, due to the absence of the yellow tip to the  
hair. If a pure agouti mouse is crossed with a black  
or non-agouti, the offspring at Fj are all agouti in  
colour — that is, the agouti factor is dominant over  
the non-agouti, which is the recessive factor. If  
however these hybrids are inbred, the F 2 generation  
comes out as 25 per cent, pure agouti, 50 per cent.  




172  
172




AIDS TO EMBRYOLOGY  
AIDS TO EMBRYOLOGY




hybrid agouti, and 25 per cent, pure non-agouti.  
hybrid agouti, and 25 per cent, pure non-agouti. This shows the Mendelian ratio of 1 : 2 : 1.
This shows the Mendelian ratio of 1 : 2 : 1.  


In both the agouti (A) and the non-agouti (b) mice  
In both the agouti (A) and the non-agouti (b) mice there is a variety with straight hair (S) and a variety with wavy hair (w). If a non-agouti wavy mouse (bw) be crossed with an agouti straight mouse (AS), the F! animals will be agouti straight (AbSw) since A is dominant over b, and S over w. Then if these F x hybrids are inbred the genes will be segregated out as follows :
there is a variety with straight hair (S) and a variety  
with wavy hair (w). If a non-agouti wavy mouse  
(bw) be crossed with an agouti straight mouse (AS),  
the F! animals will be agouti straight (AbSw) since A  
is dominant over b, and S over w. Then if these F x  
hybrids are inbred the genes will be segregated out  
as follows :  




Agouti straight (AS)  
Agouti straight (AS) Agouti wavy (Aw) Non-agouti straight (bS) Non-agouti wavy (bw) .
Agouti wavy (Aw)  
Non-agouti straight (bS)  
Non-agouti wavy (bw) .  




9  
9


3  
3


3  
3


1  
1




In these experiments two new types have been  
In these experiments two new types have been produced — the agouti wavy and the non-agouti straight. The combinations of dominant and recessive characters which have produced these adult forms are shown in Fig. 44. It will be seen that the AbSw hybrids gave rise to four gametes in equal numbers :
produced — the agouti wavy and the non-agouti  
straight. The combinations of dominant and recessive characters which have produced these adult  
forms are shown in Fig. 44. It will be seen that the  
AbSw hybrids gave rise to four gametes in equal  
numbers :  


AS : Aw : bS : bw.  
AS : Aw : bS : bw.




These combinations take place in the ova as well as  
These combinations take place in the ova as well as in the spermatozoa and since every kind of ovum is likely to be fertilised by any kind of spermatozoon, there are 4 s = 16 possible combinations yielding 9 agouti straight, 3 non-agouti straight, 3 agouti wavy and 1 non-agouti wavy. The several genes of the cross are being segregated out as is shown in Fig. 44. This rule holds good for other possible combinations.
in the spermatozoa and since every kind of ovum is  
likely to be fertilised by any kind of spermatozoon,  
there are 4 s = 16 possible combinations yielding 9  
agouti straight, 3 non-agouti straight, 3 agouti wavy  
and 1 non-agouti wavy. The several genes of the  
cross are being segregated out as is shown in Fig. 44.  
This rule holds good for other possible combinations.  


The blood groups A, B, AB and O are transmitted  
The blood groups A, B, AB and O are transmitted from parents to offspring in accordance with Mendelian laws. The principles involved may be briefly stated as follows :
from parents to offspring in accordance with Mendelian laws. The principles involved may be briefly  
stated as follows :  


When red blood corpuscles of one animal species  
When red blood corpuscles of one animal species




173  
173




HEREDITARY CHARACTERS  
HEREDITARY CHARACTERS




are mixed with the serum of another species they  
are mixed with the serum of another species they become clumped together or agglutinated. There is in the serum a substance (an agglutinin) which
become clumped together or agglutinated. There is  
in the serum a substance (an agglutinin) which  






AS  
AS


Aw  
Aw


bS  
bS


bw  
bw


Sperms  
Sperms


" J t  
" J t


A5  
A5


A A 55  
A A 55


Pure Agouti.  
Pure Agouti.


^ure  
^ure


Straight.  
Straight.


AASw  
AASw Pure Agouti. Hybrid Straight.
Pure Agouti.  
Hybrid  
Straight.  


AbS5  
AbS5


Hybrid Agouti.  
Hybrid Agouti.


Pure  
Pure


Straight.  
Straight.


AbSw  
AbSw Hybrid Agouti, | Hybrid
Hybrid Agouti, |  
Hybrid  


Straight. I  
Straight. I


Aw  
Aw


A A5w  
A A5w


Pure Agouti.  
Pure Agouti. Hybrid
Hybrid  


Straight.  
Straight.


AAww  
AAww


Pure Agouti.  
Pure Agouti. Pure Wave.
Pure Wave.  


AbSw  
AbSw


Hybrid Agouti.  
Hybrid Agouti. Hybrid Straight.
Hybrid  
Straight.  


Abww 1  
Abww 1 Hybrid j
Hybrid j  


Agouti.  
Agouti.


Pure Wave. #  
Pure Wave. #


bS  
bS


AbSS  
AbSS


Hybrid  
Hybrid Agouti .
Agouti .  


Pure  
Pure


Straight.  
Straight.


AbSw  
AbSw


4  
4


Hybrid  
Hybrid


Agouti.  
Agouti.


Hybrid  
Hybrid


Straight.  
Straight.


bbSS  
bbSS


Pure  
Pure


Mon Agouti .  
Mon Agouti . Pure
Pure  


Straight.  
Straight.


bbSw  
bbSw


Pure  
Pure


Mon Agouti .  
Mon Agouti . Hybrid Str&igW t .
Hybrid  
Str&igW t .  


bw  
bw


Ab Sw  
Ab Sw


Hybrid  
Hybrid Agouti . Hybrid Straight.
Agouti .  
Hybrid  
Straight.  


Abww  
Abww


Hybrid  
Hybrid Agout i .
Agout i .  


Pure  
Pure


Wave  
Wave


bbSw  
bbSw


Pure  
Pure


Non Agouti .  
Non Agouti . Hybrid Straight.
Hybrid  
Straight.  


bbw w  
bbw w


Pure  
Pure


Non Agouti.  
Non Agouti.


Pure  
Pure


Wave.  
Wave.




F IG . 44. — Schematic Table to show the possible Com
F IG . 44. — Schematic Table to show the possible Com BINATIONS OF THE GENES FOR STRAIGHT HAIR, WAVY
BINATIONS OF THE GENES FOR STRAIGHT HAIR, WAVY  


Hair, Agouti Colour and Non-Agouti Colour in Mice.  
Hair, Agouti Colour and Non-Agouti Colour in Mice. A = agouti ; S = straight ; b = non-agouti ; w - wavy.
A = agouti ; S = straight ; b = non-agouti ; w - wavy.  


attaches itself to an agglutinable substance (agglutinogen) in the red cells and clumping occurs.  
attaches itself to an agglutinable substance (agglutinogen) in the red cells and clumping occurs. In man, blood cannot be transfused from one person to another unless the two bloods are compatible. The important factor is the agglutinogen in the red
In man, blood cannot be transfused from one person  
to another unless the two bloods are compatible.  
The important factor is the agglutinogen in the red  




174  
174




AIDS TO EMBRYOLOGY  
AIDS TO EMBRYOLOGY




cells of the donor ; if that is incompatible with the  
cells of the donor ; if that is incompatible with the agglutinin in the recipient’s serum, serious consequences will result in transfusion. From the standpoint of heredity the A and the B agglutinogen factors are dominant over the O factor. If a child’s blood belongs to either group A or B one or other of its parents must have blood belonging to such a group.
agglutinin in the recipient’s serum, serious consequences will result in transfusion. From the standpoint of heredity the A and the B agglutinogen  
factors are dominant over the O factor. If a child’s  
blood belongs to either group A or B one or other of  
its parents must have blood belonging to such a  
group.  


Genes do not always act in the relatively simple  
Genes do not always act in the relatively simple manner just described. There may be incomplete
manner just described. There may be incomplete  




Parents  
Parents




XhY  
XhY


[H&emopluVic  
[H&emopluVic




Daughter free from  
Daughter free from disease but CAN TRANSMIT.
disease but CAN  
TRANSMIT.  






XbX?  
XbX?




Marries  
Marries




Son free from  
Son free from ® AY disease but CANNOT TRANSMIT, normd male.XY
® AY disease but  
CANNOT TRANSMIT,  
normd male.XY  




XkY <?  
XkY <?




T  
T




XwX?  
XwX?




~~\ —  
~~\ —


XX?  
XX?




“1  
“1


XY o* *  
XY o* *




fUemophi'ic Son. Daughter free Normal Daughter. Normal Son.  
fUemophi'ic Son. Daughter free Normal Daughter. Normal Son.


from disease  
from disease but CA N
but CA N  


TRANSMIT.  
TRANSMIT.




Fig. 45. — Schematic Table to show the Transmission of  
Fig. 45. — Schematic Table to show the Transmission of


HAEMOPHILIAC GENES THROUGH THREE GENERATIONS.  
HAEMOPHILIAC GENES THROUGH THREE GENERATIONS.


X, female chromosome with non-haemophiliac gene ; Xh, female  
X, female chromosome with non-haemophiliac gene ; Xh, female chromosome with haemophiliac gene ; Y, normal male
chromosome with haemophiliac gene ; Y, normal male  


chromosome.  
chromosome.


*
action of a gene or there may be a lethal gene present. An example of the latter is the disease in man called Huntingdon’s chorea. Here the disease appears first about 35 years of age and the patient rarely lives longer than ten to twelve years after that time. The carrier is eventually killed by his or her predisposition to the disease but only after he or she has passed on the lethal gene to the offspring.


action of a gene or there may be a lethal gene present.
Sex-linked characters are important in certain rare diseases such as haemophilia. The factor here is
An example of the latter is the disease in man called
Huntingdon’s chorea. Here the disease appears
first about 35 years of age and the patient rarely
lives longer than ten to twelve years after that time.  
The carrier is eventually killed by his or her predisposition to the disease but only after he or she
has passed on the lethal gene to the offspring.


Sex-linked characters are important in certain rare
diseases such as haemophilia. The factor here is


175


175


HEREDITARY CHARACTERS


HEREDITARY CHARACTERS
transmitted on an X chromosome. If a haemophiliac male marries a normal unrelated female all their daughters must necessarily receive one haemophiliac X chromosome from the father and a normal X chromosome from the mother. The sons all receive a normal Y chromosome from the father and a normal X chromosome from the mother. They therefore do not suffer from the disease, nor can they transmit it to their offspring. But the daughters all have a haemophilac X chromosome, and they will necessarily transmit the disease to 50 per cent, of their sons after marriage with a normal male.


transmitted on an X chromosome. If a haemophiliac
male marries a normal unrelated female all their
daughters must necessarily receive one haemophiliac
X chromosome from the father and a normal X
chromosome from the mother. The sons all receive a normal Y chromosome from the father and
a normal X chromosome from the mother. They
therefore do not suffer from the disease, nor can
they transmit it to their offspring. But the daughters
all have a haemophilac X chromosome, and they will
necessarily transmit the disease to 50 per cent, of
their sons after marriage with a normal male.


APPENDIX


APPENDIX
OSSIFICATION TIMES


OSSIFICATION TIMES
The ossification periods have been widely studied, but the work of Hess (i9 2 3)> although differing in some respects from that usually given in textbooks on osteology, is now recognized as being the most accurate series of observations at present available. These observations may be summarized as follows :


The ossification periods have been widely studied,
7th week : Mandible, diaphysis of clavicle.
but the work of Hess (i9 2 3)> although differing in
some respects from that usually given in textbooks on
osteology, is now recognized as being the most accurate series of observations at present available.  
These observations may be summarized as follows :


7th week : Mandible, diaphysis of clavicle.  
8th week : Diaphysis of humerus, radius, and ulna. 9th week : The terminal phalanges, the 2nd and 3rd basal phalanges, and the 2nd and 3rd metacarpal bones of the hand ; the ilium ; the 2nd and 3rd metatarsals, and the terminal phalanges of the foot bones.


8th week : Diaphysis of humerus, radius, and ulna.
10th week : 1st rib, and the 4th and 1st basal phalanges of the hand.
9th week : The terminal phalanges, the 2nd and 3rd
basal phalanges, and the 2nd and 3rd metacarpal
bones of the hand ; the ilium ; the 2nd and 3rd
metatarsals, and the terminal phalanges of the
foot bones.  


10th week : 1st rib, and the 4th and 1st basal phalanges of the hand.  
10th to 12th week : 4th, 5th, and 1st metatarsals.


10th to 12th week : 4th, 5th, and 1st metatarsals.


176 AIDS TO EMBRYOLOGY


176 AIDS TO EMBRYOLOGY
nth to 1 2th week : The basal phalanx of the 5th digit, and the middle phalanges of the 2nd, 3rd, and 4th digits of the hand.


nth to 1 2th week : The basal phalanx of the 5th
13th to 14th week : All the remaining metatarsals and the phalanges of the foot except the last phalanx of the 5th digit.
digit, and the middle phalanges of the 2nd, 3rd,
and 4th digits of the hand.  


13th to 14th week : All the remaining metatarsals and
13th to 1 6th week : The middle phalanx of the 5th finger.
the phalanges of the foot except the last phalanx  
of the 5th digit.  


13th to 1 6th week : The middle phalanx of the 5th
1 6th to 17th week : Descending ramus of ischium.
finger.  


1 6th to 17th week : Descending ramus of ischium.  
17th to 20th week : Odontoid process of axis.


17th to 20th week : Odontoid process of axis.  
2 1st to 24th week : Sternum.


2 1st to 24th week : Sternum.  
2 1st to 28th week : Descending ramus of pubis.


2 1st to 28th week : Descending ramus of pubis.  
2 1st to 29th week : Calcaneus (os calcis).


2 1st to 29th week : Calcaneus (os calcis).  
24th to 32nd week : Talus (astragalus).


24th to 32nd week : Talus (astragalus).  
33rd to 36th week : Last phalanx of the 5th digit of foot.


33rd to 36th week : Last phalanx of the 5th digit of
35th to 48th week : Distal epiphysis of femur, and occasionally the proximal epiphysis of tibia.
foot.
 
35th to 48th week : Distal epiphysis of femur, and  
occasionally the proximal epiphysis of tibia.
 
The wide variation in these figures might be accounted for by the statement of Pryor (1927), that
 
ossification begins at an earlier date in female foetuses
 
than in the male.
 
 
INDEX
 
 
Accessory tubercle of pinna, 74
Acoustico-facial complex, 71
Acrocephaly, 167
Acrosome, 3
Adrenal gland, 61
Alimentary canal, 75
Allantois, 34, 141, 142
Amnion, 15, 32
Amnio tic cavity, 15, 16
fluid, 33
Amastia, 43
Anencephaly, 59
Angiogenesis, 34
Aorta, branches of, 114
coarctation of, 118
Aortic arches, 109
trunk, 105
 
Appendicular skeleton, 166
Appendix, 92
Artery or arteries,
axial, lower limb, 116
femoral, 116
intersegmental, 113
pulmonary, 117
radial, 115
ulnar, 115
of upper limb, 115
anomalies of, 118
development of, 116
Atresia, of aorta, 108
intestinal, 93
of pulmonary artery, 108
Atria, development of, 104
Atrio-ventricular bundle, 106
Auditory apparatus, development of, 73
Auditory nerve, 71
ossicles, 74
 
Autonomic nervous system, 61
Axial skeleton, 161
 
 
Bicornuate uterus, 151
Bipartite uterus, 151
Bladder, development of, 143
Blastocyst, 14
Blood cells, 130
Body stalk, 99
 
 
Bone, histogensis of, 159
Bony labyrinth, 72
Bowman’s capsule, 140
Brain, development of, 58
Branchial arch arteries, 109
Branchio-motor cells, 52
Breast, anomalies of, 43
Buccopharyngeal membrane,
36, 75
 
Bulbus cordis, 100
 
 
Caecum, 90, 92
Canal of Schlemm, 66
Cardiogenic area, 100
Carotid body, 112
sinus, 1 12
 
Central nervous system,
anomalies of, 59
Cerebral aqueduct, 53
commissures, 56
cortex, 57
Cervix, 148
Chorion, 29, 99
frondosum, 31
laeve, 31
Choroid, 66
Chromaffin cells, 61
Chromosomes, 9
Circulation, at birth, 128
foetal, 128
 
Circulatory system, 99
Cleft palate, 86
sternum, 167
 
Clitoris, hypertrophy of, 155
Cloaca, 1 41
persistent, 144
Cloacal membrane, 75
Club-foot, congenital, 167
Coarctation of aorta, 118
Cochlea, 71, 73
 
Coelom, extra-embryonic, 19
Coelomic cavities, 132
Coloboma, congenital, 67
Colon, 92
Cornea, 66
Corona radiata, 8
Coronary sinus, 105
 
1 77
 
 
12
 
 
AIDS TO EMBRYOLOGY
 
 
178
 
Corpus albicans, 21
callosum, 57
luteum, 20, 21
striatum, 56
Corti, organ of, 72
Cotyledons, 31
Crista acoustica, 71
Cyclopia, 68
 
Cystic kidney, congenital, 140
Cuvier, duct of, 119
 
Deafness, congenital, 74
Decidua capsularis, 29, 31
Deciduous teeth, 80
Dental fibrils of Tomes, 81
papilla, 80
Dextrocardia, 108
Diencephalon, 48, 53
Dorsal aorta, branches of, 112
Double heart, 108
Ductus arteriosus, no
persistence of, 118
Ductus reuniens, 71
Duodenal stenosis, 93
Duodenum, 91
Dura mater, 58
Dwarfism, 167
 
Dysostosis cleido-cranialis, 167
 
Ear, anomalies of, 74
Ectoderm, 35, 3 8
Ectopia testis, 153
vesicae, 144
Embryo, 15
age of, 38
Embryonic axis, 1 7
disc, 17
mesoderm, 18
Encephalocoele, 59
Endochondrial ossification, 159
Entoderm, 35, 3 8
Epibranchial placodes, 7 5
Epididymis, duct of, 146
Epiglottis, 99
Epispadias, 155
Epoophoron, 148
Eye, 63
 
congenital cystic, 68
development of, 67
Eyelids, 66
 
 
Face, 77
 
anomalies of, 85
Facial cleft, oblique, 86
Femoral artery, 116
Fertilization, 24
Foetal age, estimation of, 39
Foetal circulation, 128
Follicular atresia, 8, 20
Follicle stimulating
hormone, 20, 23
Foramen, caecum, 79
of Majendie, 52
ovale, 108
 
patent interventricular, 108
 
 
Gall bladder, 94
Gartner, duct of, 148
Genitalia, female, 154
male, 153
Genetics, 169
Genital glands, descent
of, 151
 
Genital glands and ducts, 144
Genital system, anomalies
of, 151
 
development of, 150
Genitals external, 154
Germinal epithelium, 5
Gigantism, 167
Glaucoma, congenital, 68
Glycogen, 23
Gonads, 151
Graffian follicle, 6
Gubemaculum, 15 1
Gut, fore, 75
hind, 75
mid, 75
primitive, 87
Gynaecomastia, 43
 
 
Haemocytoblasts, 131
Hair, 41
Hare lip, 86
Haploid number, 13
Heart, 100
 
anomalies of, 108
development of, 107
valves, 106
Hensen’s node, 17, 18
 
 
INDEX
 
 
179
 
 
Hereditary characters, 168
Hermaphroditism, 155
Hernia, congenital
inguinal, 153
Hippocampal gyrus, 57
Hormone, follicle
stimulating, 20
luteal, 21, 23
Horseshoe kidney, 14 1
Hyaloid artery, 66
Hydrochloric acid, 89
Hydramnios, 34
Hydrocephalus, congenital, 59
Hymen, 149, 150
imperforate, 151
Hyoid arch, 76
Hypermastia, 43
Hypophysis, 54
Hypospadias, 155
 
 
Imperforate hymen, 151
Implantation, 26
interstitial, 28
Incus, 72
 
Infundibulum, 55
Inferior vena cava, 122, 128
Interatrial septa, 102
Interventricular septum, 105
Intestine, 89
 
non-rotation of, 94
Intestinal atresia, 93
Intestinal tract, anomalies of, 93
Iris, 67
 
 
Kidney, development of, 140
pelvic, 14 1
 
 
Labia minora, hypertrophy of,
155
 
Lachrymal glands, 66
Lactiferous ducts, 43
Lamina, alar, 48, 51
basal, 48, 51
Lanugo, 42
Lens, 64
 
Ligament of Marshall, 122
Limb muscles, 158
Lissauer’s bundle, 46
 
 
Liver, 89, 94
 
anomalies of, 98
development of, 97
Lymphatic vessels and
glands, 129
Lymphoblasts, 131
 
Malleus, 72
 
Majendie, foramen of, 7 2
Mammary glands, 42
Mandible, 162
Marshall, ligament of, 122
Maxillary process, 162
Meckel’s cartilage, 72
diverticulum, 93
Medulla oblongata, 49
Mendelian laws, 171
Meninges, 58
Meningocoele, 59
Menstruation, 21
Mesencephalon, 48, 53
Mesoderm, 35
 
extra-embryonic, 19
Mesogastrium, dorsal, 89
Mesonephros, 136
Metanephros, 138
Metencephalon, 49, 52
Microcephaly, 59
Mid-brain flexure, 51
Milk teeth, 80
Mitosis, 8
Mucin, 23
 
Mullerian duct, 146
tubercle, 146
Myelencephalon, 49, 51
Myelocytes, 131
Myotomes, 157
 
Nails, 41
 
Naso-lachrymal duct, 41
groove, 77
 
Nerve, abducent, 60, 62
auditory, 60
facial, 60, 62
glossopharyngeal, 60, 62
hypoglossal, 60, 62
oculomotor, 60, 62
olfactory, 60
optic, 60
 
trigeminal, 60, 62
 
trochlear, 60, 62
 
vagus and accessory, 60, 62
 
 
i8o
 
 
AIDS TO EMBRYOLOGY
 
 
Neuroblasts, 48
Neurocranium, 162
Neuroglia, 48
Notochord, 35
Notochordal canal, 17
Nucleus ambiguus, 51
 
 
Oesophagus, 88
Oestrogen, 23
Olfactory organ, 63
pit, 77
tract, 57
Oligamnios, 34
Oogenesis, 6
Optic cup, 63
Oro-nasal groove, 77
Ossicles, auditory, 74
Osteoblasts, 159
Osteoclasts, 159
Otocyst, 69
 
Ovaries, absence of, 151
Ovary, 5
 
round ligament of, 153
 
 
Palate, 78
Palatine tonsil, 85
Pancreas, 95
anomalies of, 98
development of, 97
Paradidymis, 147
Parathyroids, 84
Parotid gland, 82
Paroophorn, 148
Patent interventricular
foramen, 108
Pelvic kidney, 141
Penis, double, 155
Pericardial cavity, 132
Peripheral nervous system, 62
Persistent foramen ovale, 108
Pharyngeal region, 75
anomalies of, 85
development of, 85
Pharyngeal grooves, 83
pouches, 83
 
Pharyngo-tympanic tube, 74
Phimosis, 155
Pineal gland, 54
Pinna, 73
 
accessory tubercles of, 74
 
 
Pituitary gland, 54
Placenta, 15, 31
Placodes, epibranchial, 75
Plagiocephaly, 167
Pleural cavities and
diaphragm, 134
Polydactyly, 167
Pontine nuclei, 52
Prepuce, 155
Primitive atrium, 100
ventricle, 100
Processus vaginalis, 15 1
Progesterone, 20, 24
Pronephros, 136
Pronucleus, female, 13
male, 12
 
Prostate gland, 142
Pulmonary arteries, 117
trunk, 105
 
Puncta lachrymalia, 68
 
 
Rachischisis, 59, 166
Rathke’s pouch, 55
Rectum, malformations
of, 93
 
Reichert’s cartilage, 72
Rennin, 89
 
Respiratory system, 98
 
Rhombic lip, 52
 
Ribs, supernumerary, 166
 
 
Saccule, 73
Salivary glands, 82
Scaphocephaly, 167
Schlemm, canal of, 66
Schlera, 66
Schlerotomes, 161
Scrotum, 15 1
Sebaceous glands, 42
Segmentation nucleus, 13
Septum, posterior median, 48
transversum, 36
Sinus, inferior sagittal, 120
superior sagittal, 120
venosus, 100, 105
Situs inversus, 94
Skeleton, anomalies of, 166
Skin, 40
Skull, 1 61
Somites, 157
 
 
INDEX
 
 
181
 
 
Spermatogenesis, 2, 26
Spermatozoon, 4, 26
Sphenoid, 162
Spinal cord, 46
anomalies of, 48
development of, 47
Spinal nerves, 59
Splanchnopleure, 19
Spleen, 131
Split tongue, 86
Spongioblasts, 48
Stomach, 88
Stomatodaeum, 36, 77
Stenosis of aorta, 108
 
of pulmonary artery, 108
Stratum basale, 22
spongiosum, 21
Sublingual gland, 82
Submandibular gland, 82
Sudoriferous glands, 42
Sulcus, calcarine, 58
central, 58
collateral, 58
hypothalamieus, 53
limitans, 53
terminahs, 79
Superior vena cava, 128
Sweat glands, 42
Syndactyly, 167
Synotus, 74
 
 
Teeth, decidual or milk, 80
enamel of, 80
permanent, 80
Telencephalon, 48, 55
Testis, 1, 145
absence of, 151
fused, 15 1
Thalamus, 53
Theca interna, 7
Thymus, 83
Thyro-glossal duct, 79
Thyroid, 84
 
Tomes’ dental fibrils, 81
Tongue, 79
split, 86
Tonsils, 83
Trabeculae, 95
Trophoblast, 15
Tunica albuginea, 145
 
 
Tympanic antrum, 74
cavity, 72
membrane, 73
 
 
Umbilical cord, 31, 35
hernia, congenital, 93
veins, 95
 
Urachus, cysts of, 144
Ureter, 140
double, 1 41
Ureteric bud, 140
Urethra, 142
stenosis of, 155
Urorectal septum, 141
Uterine milk, 5, 148
tubes, 5, 148
Uterus, 5
 
round ligament of, 153
 
 
\
 
 
Vagina, anomalies of, 151
Valves, atrio-ventricular, 105
Vas deferens, 147
Vasa efferentia, 147
Veins, anterior cardinal, 119
posterior cardinal, 122
anomalies of, 128
Vena cava, inferior, 105
superior, 105
Venous system, 118
development of, 126
 
Villi, 15
 
anchoring, 30
chorionic, 29
Viscerocranium, 164
Vitreous humour, 66
Vocal cords, 99
 
 
Wharton’s jelly, 35
Witch’s milk, 43
 
 
Yolk sac, I 5 -I 7 , 34 , 99
 
 
Zona pellucida, 6,
Zygote, 12
 
 
12, 15
 
 
 
PRINTED IN GREAT BRITAIN AT
THE UNIVERSITY PRESS
ABERDEEN
 
 
 
 
STUDENTS’
 
AIDS
 
SERIES
 
 
 
 
The Students' Aids Series is the
most complete set of small textbooks published in this or any
other country.
 
^ #
 
It provides clear, concise and readable textbooks on a wide variety of
subjects.
 
* % * *
 
Each volume is authoritative, a
guide to its subject and, as the title
suggests, an “ AID ” to its study.
Many volumes are complete textbooks in themselves.
 
# * # #
 
Since its foundation in 1876, the
Students' Aids Series has proved
absolutely indispensable to each
succeeding generation of students.
 
Uniform Size 4" X
Postage : 3 d. each volume
 
 
BAILLIERE, TINDALL & COX
7 and 8, Henrietta Street, London, W.C.2
 
 
 
STUDENTS’ AIDS SERIES
 
 
AIDS TO BIOLOGY. By R. G. Neill, M.A. Second Ed.
Pp. viii + 279, with 21 figs. 6s.
 
AIDS TO BOTANY. By H. J. Bonham, B.Sc. Second Ed.
Pp. viii + 216, with 57 figs. 6s.
 
 
AIDS TO ZOOLOGY. By H. Lister, M.Sc., F.Z.S. Third
Ed. Pp. vii + 259, with 52 figs. 6s.
 
AIDS TO ANATOMY. By E. P. Stibbe, F.R.C.S. Tenth Ed.
Pp. viii + 370, with 50 figs. 5 s. 6d.
 
AIDS TO PHYSIOLOGY. By H. Dryerre, Ph.D., M.R.C.S.
Third Ed. Pp. viii + 3°6, with 63 figs. 4 s. 6d.
 
AIDS TO HISTOLOGY. By A. Goodall, M.D., F.R.C.P.
(Edin.). Fourth Ed. Pp. viii + 15 1, with 26 figs. 4 s.
 
AIDS TO OSTEOLOGY. By N. L. Eckhoff, M.S., F.R.C.S.
Fourth Ed. Pp. viii + 260, with 42 figs. 5 s.
 
AIDS TO PATPIOLOGY. By J. O. Oliver, M.B., B.S.,
M.R.C.S. Ninth Ed. Pp. vii + 332 , with 14 figs. 7 s. 6d.
 
AIDS TO CLINICAL PATHOLOGY. By D. Haler, M.B.,
B.S. Pp. viii + 358, with 21 figs. 6s.
 
AIDS TO EMBRYOLOGY. By J. S. Baxter, M.Sc., M.D.,
F.R.C.S. I. Fourth Ed. Pp. viii + 181, with 45 figs. 5 s.
 
 
AIDS TO OBSTETRICS. By Leslie Williams, M.D.,
F.R.C.S. Eleventh Ed. Pp. viii + 238, with 10 figs. 4 s.
 
AIDS TO GYNAECOLOGY. By W. R. Winterton, M.B.,
B.Ch., F.R.C.S., M.R.C.O.G. Tenth Ed. Pp. vm + 184.
 
5 s.
 
v
 
AIDS TO MEDICINE. By J. L. Livingstone, M.D., F.R.C.P.
Fifth Ed. Pp. viii + 422. 5 s. 6d.
 
AIDS TO BACTERIOLOGY. By H. W. Scott-Wilson,
B.Sc., B.M., B.Ch. Seventh Ed. Pp. viii + 300* 6 s.
 
AIDS TO SURGERY. By Cecil A. Joll, M.S., F.R.C.S., and
R. C. B. Ledlie, F.R.C.S. With 58 illustrations by H. H.
Greenwood, F.R.C.S. Seventh Ed. Pp. xii + 654. 10 s.
 
AIDS TO OPERATIVE SURGERY. By Sir Cecil Wakeley,
K.B.E., C.B., D.Sc., F.R.C.S., F.R.S. Second Ed. Pp.
viii + 226, with 3 illustrations. 4s *
 
AIDS TO ORTHOPAEDIC SURGERY AND FRACTURES.
By J. E. Zieve, M.A., F.R.C.S. Third Ed. In preparation.
 
AIDS TO SURGICAL ANATOMY. By J. S. Baxter, M.Sc.,
F.R.C.S. I. Second Ed. Pp. viii + 193, with 26 figs.
 
4 s. 6d.
 
 
AIDS TO MATERIA MEDICA. By G. H. Newns, M.D.,
M.R.C.P. Third Ed. Pp. viii + 21 1. 5 s.
 
AIDS TO FORENSIC MEDICINE AND TOXICOLOGY.
By J. H. Ryffel, B.Ch., B.Sc. Twelfth Ed. In preparation.
 
 
STUDENTS’ AIDS SERIES (continued)
 
AIDS TO ANAESTHESIA. By Victor Goldman, M.R.C S
 
L. R.C.P., D.A. Second Ed. Pp. viii + 278. 7 s. 6d.
 
AIDS TO MEDICAL TREATMENT. By T. II. Crozier,
 
M. D., D.P.H., M.R.C.P. Second Ed. In preparation .
 
AIDS TO MEDICAL DIAGNOSIS. By G. E. F. Sutton,
M.C., M.D., M.R.C.P. Sixth Ed. Pp. viii + 308, with 40
 
figs. 6s *
 
AIDS TO SURGICAL DIAGNOSIS. By Sir Cecil Wakeley,
K.B.E., C.B., D.Sc., F.R.C.S., F.R.S. Second Ed. Pp.
viii + 172, with 6 figs.
 
AIDS TO DERMATOLOGY. By R. M. B. MacKenna, M.D.,
B Ch., F.R.C.P. Third Ed. Pp. viii + 3°9, with 5 figs. 6s.
 
AIDS TO DISEASES OF CHILDREN. By F. M. B. Allen,
M.D., F.R.C.P. Eighth Ed. Pp. viii + 268. 6s.
 
AIDS TO NEUROLOGY. By E. A. Blake Pritchard, M.D.,
M.R.C.P. Pp. viii + 376, with 43 figs. os. 6a.
 
AIDS TO OPHTHALMOLOGY. By P. McG. Moffatt,
F.R.C.S. Eleventh Ed. 6s * 6d *
 
AIDS TO PSYCHIATRY. By W. S. Dawson, M.D., F.R.C.P.,
D.P.M. Fifth Ed. Pp. viii + 306. 6s.
 
AIDS TO PSYCHOLOGY. By John H. Ewen, M.R.C.S.,
M.R.C.P., D.P.M. Third Ed. In preparation.
 
AIDS TO TROPICAL MEDICINE. By J. C. Broom, M.D.
Fourth Ed. Pp. viii + 203, with 30 figs. 5 s.
 
AIDS TO TROPICAL HYGIENE. Edited by Lucius
Nicholls, M.D., Third Ed. Pp. viii + 217, with 6 figs. 6 s.
 
AIDS TO THE DIAGNOSIS AND TREATMENT OF
VENEREAL DISEASES. By T. E. Osmond, M.B.,
M.R.C.S. Pp. vi + 138, with 3 figs. 5s *
 
 
AIDS TO THE ANALYSIS OF FOODS AND DRUGS. By
J. R. Nicholls, D.Sc., F.I.C. Sixth Ed. Pp. via + 424
I US.
 
AIDS TO QUALITATIVE INORGANIC ANALYSIS By
R. G. Austin, B.Sc., F.R.I.C., F.R.M.S. Second Ed.
Pp. x + 208, with 9 illustrations. 5s *
 
AIDS TO BIOCHEMISTRY. By E. A. Cooper, D.Sc.,
F.R.I.C. Fourth Ed.
 
AIDS TO INORGANIC CHEMISTRY. By R. G. Austin,
B.Sc., F.R.I.C., F.R.M.S. Pp. x + 348, with 6 ngs. 5 s. 6d.
 
AIDS TO ORGANIC CHEMISTRY. By S. F. Smith, M.B.,
B.S. Third Ed. Revised by Ian Leslie, B.Sc. Pp. vui + 120.
 
 
AIDS TO PHYSICAL CHEMISTRY. By R. G. Austin,
B.Sc., F.R.I.C., F.R.M.S. Second Ed. In preparation .
 
AIDS TO DISPENSING. By G. M. Watson. Fourth Ed,
 
In preparation .
 
 
STUDENTS’ AIDS SERIES (continued)
 
AIDS TO PHARMACEUTICAL LATIN. By G. E. Trease,
B.Pharm., Ph.C. Second Ed. Pp. vi + 170. 4 s.
 
AIDS TO FORENSIC PHARMACY. By M. E. Campbell,
Fourth Ed. In preparation.
 
AIDS TO THE MATHEMATICS OF PHARMACY. By
A. W. Lupton, M.C., Ph.C. Second Ed. Pp. vi + 122. 4 s.
 
AIDS TO PHYSICS. By F. J. Jackson, B.Sc., Ph.C., M.P.S.
2 vols. In preparation.
 
AIDS TO PUBLIC HEALTH. By Llywelyn Roberts, M.D.,
D.P.H. Fifth Ed. Pp. viii 4- 259, with 4 figs. 6s.
 
AIDS TO SANITARY SCIENCE AND LAW. Revised by
William Hanna, M.D., D.P.H. Third Ed. Pp. vi 4- 362.
 
5 s. 6d.
 
 
OTHER BOOKS
 
HANDBOOK OF BACTERIOLOGY. By J. W. Bigger,
M.D., Se.D.(DubL). Sixth Ed. In preparation.
 
BUCHANAN’S MANUAL OF ANATOMY. Edited by
F. Wood Jones, D.Sc., F.R.S., F.R.C.S. Seventh Ed. Pp.
viii 4 - 1616, with 847 illustrations. 45 s.
 
ELECTROTHERAPY AND ACTINOTHERAPY FOR
STUDENTS. By E. Bellis Clayton, M.B., B.Ch.
 
In preparation.
 
GREEN’S MANUAL OF PATHOLOGY. Revised by
H. W. C. Vines, M.A., M.D. Seventeenth Ed. In preparation.
 
A METHOD OF ANATOMY. By J. C. B. Grant, M.B.,
Ch.B., F.R.C.S. Third Ed. Pp. xxiv + 822, with 729
illustrations. 33s.
 
DISEASES OF THE SKIN. By R. W. MacKenna, M.D.,
M.R.C.P. Fourth Ed. Pp. xiv + 557, with 214 illustrations. 25 s.
 
MAY & WORTH’S DISEASES OF THE EYE. Edited by
M. L. Hine, M.D., F.R.C.S. Tenth Ed. In preparation.
 
ROSE & CARLESS’ MANUAL OF SURGERY. Edited by
Sir Cecil Wakeley, K.B.E., C.B., D.Sc., F.R.C.S., F.R.S.
Seventeenth Ed. 2 Vols. Vol. I. Pp. xii + 840. Vol. II.
Pp. iv 4 - 926, with 1130 illustrations. 35 s.
 
STEDMAN’S PRACTICAL MEDICAL DICTIONARY.
Edited by N. B. Taylor, M.D. Sixteenth Ed. Pp. xii 41292, with 450 illustrations. 42 s.
 
 
For further information on these and other Bailliire books, please apply to  the publishers.


The wide variation in these figures might be accounted for by the statement of Pryor (1927), that ossification begins at an earlier date in female foetuses than in the male.






{{Baxter1948 footer}}
{{Baxter1948 footer}}

Revision as of 15:51, 25 October 2018

Embryology - 26 Apr 2024    Facebook link Pinterest link Twitter link  Expand to Translate  
Google Translate - select your language from the list shown below (this will open a new external page)

العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt    These external translations are automated and may not be accurate. (More? About Translations)

Baxter JS. Aids to Embryology. (1948) 4th Edition, Bailliere, Tindall And Cox, London.

   Aids to Embryology 1948: 1. Germ Cells | 2. Segmentation and Germ Layer Formation | 3. Changes in Female Genital Tract | 4. Implantation and Placentation | 5. Formation of the Embryo | 6. Skin and Accessory Structures | 7. Nervous System | 8. Special Sense | 9. Alimentary Canal | 10. Circulatory System | 11. Coelomic Cavities | 12. Urogenital System | 13. Muscular and Skeletal Systems | 14. Hereditary
Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Chapter XIV The Transmission of Hereditary Characters

Every potential individual, that is, every fertilised ovum, commences development with a complement of hereditary factors (genes) derived from both parents at the time of union of the germ cells in fertilisation. These inherited factors operate during development, both before and after birth, to produce an individual resembling the parents. The environment, both prenatal and post-natal, may influence some of these hereditary characters and modify them, but there are certain characters which cannot be affected by the environment and hence are said to be determined at fertilisation. Examples of these are the blood group to which the person belongs and the colour of the eyes. The study of these hereditary factors, and the laws which govern their transmission from parents to offspring, is known as the science of genetics.


HEREDITARY CHARACTERS 169


Genetic laws are fundamentally the same for plants and animals, and since many generations of plants and lower animals can be investigated in a relatively short period of time, the study of genetics has largely been based on them. In addition, certain forms possess chromosomes particularly favourable to the genetic analysis of experimental procedures. But in all cases where genetic laws have been tested in lower forms they have been found applicable to human hereditary.


Parent ^ Tfc\l (T) "H Dw&rf (d)

fj. AU hybrid Tidls (Td)

1 ^ l


Td


Td


Hybrid Tidls


dd

Pure Dvj&rfs


1 1 1 r

Td Td dd TT


1


i


d Td dd


k dd All Pure Ow^ris


y IG< 42 . — Schematic Table showing Mendelian Inheritance AS APPLIED TO TALL AND DWARF PEAS.

T = tall ; d = dwarf.


The fundamental genetic laws are based on the experiments of Mendel (1866) on garden peas. Mendel studied the inheritance of a number of characters of this form, of which tallness and dwarfness may be taken as a typical example. If a tall pea and a dwarf pea were cross-fertilised and the resultant peas planted, all of the plants that grew from them were tall. These he called the first filial generation (Fj). These tall cross-bred plants were allowed to produce peas by self-fertilisation, and when such were sown the second filial generation (F a ) showed some plants that were tall and some that were dwarf,


AIDS TO EMBRYOLOGY


170

in the proportion of three tall to one dwarf. Peas derived from self-fertilisation of each of the dwarf plants were then sown, and they produced dwarf plants only ; seed from some of the self -fertilised tall plants produced both tall and dwarf offspring, in the proportion of three tall to one dwarf ; the remainder of the seed from the tall plants produced nothing but tall offspring in the third (F s ) generation (see Fig. 42 for details).

From these experiments it is clear that an attempt was being made by nature to separate the original pure characters of tallness and dwarfness in the


Parents

— Y

+ dd

4

P&rent G&mefes

T

»

d

j 1

F 1


.Td

Fj. Q&metes

_T.

d. T. d.


F t T ~ v7~ 1 ' >

F * TT. Td. Td. dd.

Fig. 43. — Schematic Table to show Segregation of the Tall and Dwarf Genes in the Gametes of Peas.

T = tall ; d = dwarf.

parent stock from the hybrids. This is known as the law of segregation. The character of tallness, which was found in the F x generation, is known as a dominant character since it overshadows the recessive character of dwarfness. These characters are known to be caused by certain elements on the maternal and paternal chromosomes called genes.

Consideration of Fig. 43 will indicate how these dominant and recessive factors become separated out during breeding. The parent stock possessed either the character of tallness or dwarfness in pure form, that is, when self -fertilised they always bred true. The first filial generation (Fj) were all tall since the


HEREDITARY CHARACTERS 171

gene for dwarfness was present but masked by the dominant tall (T) gene. The gametes (sex cells) of the Fj generation contained the genes for tallness and dwarfness in equal numbers so that when such plants were self-fertilised the dominant T gene would be present in three out of four of the offspring and they would all be tall plants. In one out of the four, two d (dwarfness) genes would be present and hence these plants would be dwarfs, and on further selffertilisation would continue to breed truly dwarf. One of the three tall plants would contain only genes for tallness and so on self-fertilisation it would continue to breed true for the character of tallness. The remaining two tall plants contained Td genes, and further inbreeding of them would result in the formation of dominant and recessive forms in the ratio of three dominant to one recessive.

In human genetics there are certain clear-cut cases of inheritance due to dominant factors. Examples of these are congenital brachydactyly, syndactyly, and congenital night blindness. Also black hair colour is dominant over brown hair colour, and so is brown iris colour over blue.

Mendelian laws have been applied to animals and they have been found to hold equally good for them. For example, the colour of the ordinary brownishgrey wild mouse is due to bands of pigment in its hair ; black at the base and yellow at the tip. This is known as “ agouti ” colouration. But in fancy mice there is a variety in which the hair appears black, due to the absence of the yellow tip to the hair. If a pure agouti mouse is crossed with a black or non-agouti, the offspring at Fj are all agouti in colour — that is, the agouti factor is dominant over the non-agouti, which is the recessive factor. If however these hybrids are inbred, the F 2 generation comes out as 25 per cent, pure agouti, 50 per cent.


172


AIDS TO EMBRYOLOGY


hybrid agouti, and 25 per cent, pure non-agouti. This shows the Mendelian ratio of 1 : 2 : 1.

In both the agouti (A) and the non-agouti (b) mice there is a variety with straight hair (S) and a variety with wavy hair (w). If a non-agouti wavy mouse (bw) be crossed with an agouti straight mouse (AS), the F! animals will be agouti straight (AbSw) since A is dominant over b, and S over w. Then if these F x hybrids are inbred the genes will be segregated out as follows :


Agouti straight (AS) Agouti wavy (Aw) Non-agouti straight (bS) Non-agouti wavy (bw) .


9

3

3

1


In these experiments two new types have been produced — the agouti wavy and the non-agouti straight. The combinations of dominant and recessive characters which have produced these adult forms are shown in Fig. 44. It will be seen that the AbSw hybrids gave rise to four gametes in equal numbers :

AS : Aw : bS : bw.


These combinations take place in the ova as well as in the spermatozoa and since every kind of ovum is likely to be fertilised by any kind of spermatozoon, there are 4 s = 16 possible combinations yielding 9 agouti straight, 3 non-agouti straight, 3 agouti wavy and 1 non-agouti wavy. The several genes of the cross are being segregated out as is shown in Fig. 44. This rule holds good for other possible combinations.

The blood groups A, B, AB and O are transmitted from parents to offspring in accordance with Mendelian laws. The principles involved may be briefly stated as follows :

When red blood corpuscles of one animal species


173


HEREDITARY CHARACTERS


are mixed with the serum of another species they become clumped together or agglutinated. There is in the serum a substance (an agglutinin) which


AS

Aw

bS

bw

Sperms

" J t

A5

A A 55

Pure Agouti.

^ure

Straight.

AASw Pure Agouti. Hybrid Straight.

AbS5

Hybrid Agouti.

Pure

Straight.

AbSw Hybrid Agouti, | Hybrid

Straight. I

Aw

A A5w

Pure Agouti. Hybrid

Straight.

AAww

Pure Agouti. Pure Wave.

AbSw

Hybrid Agouti. Hybrid Straight.

Abww 1 Hybrid j

Agouti.

Pure Wave. #

bS

AbSS

Hybrid Agouti .

Pure

Straight.

AbSw

4

Hybrid

Agouti.

Hybrid

Straight.

bbSS

Pure

Mon Agouti . Pure

Straight.

bbSw

Pure

Mon Agouti . Hybrid Str&igW t .

bw

Ab Sw

Hybrid Agouti . Hybrid Straight.

Abww

Hybrid Agout i .

Pure

Wave

bbSw

Pure

Non Agouti . Hybrid Straight.

bbw w

Pure

Non Agouti.

Pure

Wave.


F IG . 44. — Schematic Table to show the possible Com BINATIONS OF THE GENES FOR STRAIGHT HAIR, WAVY

Hair, Agouti Colour and Non-Agouti Colour in Mice. A = agouti ; S = straight ; b = non-agouti ; w - wavy.

attaches itself to an agglutinable substance (agglutinogen) in the red cells and clumping occurs. In man, blood cannot be transfused from one person to another unless the two bloods are compatible. The important factor is the agglutinogen in the red


174


AIDS TO EMBRYOLOGY


cells of the donor ; if that is incompatible with the agglutinin in the recipient’s serum, serious consequences will result in transfusion. From the standpoint of heredity the A and the B agglutinogen factors are dominant over the O factor. If a child’s blood belongs to either group A or B one or other of its parents must have blood belonging to such a group.

Genes do not always act in the relatively simple manner just described. There may be incomplete


Parents


XhY

[H&emopluVic


Daughter free from disease but CAN TRANSMIT.


XbX?


Marries


Son free from ® AY disease but CANNOT TRANSMIT, normd male.XY


XkY <?


T


XwX?


~~\ —

XX?


“1

XY o* *


fUemophi'ic Son. Daughter free Normal Daughter. Normal Son.

from disease but CA N

TRANSMIT.


Fig. 45. — Schematic Table to show the Transmission of

HAEMOPHILIAC GENES THROUGH THREE GENERATIONS.

X, female chromosome with non-haemophiliac gene ; Xh, female chromosome with haemophiliac gene ; Y, normal male

chromosome.

action of a gene or there may be a lethal gene present. An example of the latter is the disease in man called Huntingdon’s chorea. Here the disease appears first about 35 years of age and the patient rarely lives longer than ten to twelve years after that time. The carrier is eventually killed by his or her predisposition to the disease but only after he or she has passed on the lethal gene to the offspring.

Sex-linked characters are important in certain rare diseases such as haemophilia. The factor here is


175


HEREDITARY CHARACTERS

transmitted on an X chromosome. If a haemophiliac male marries a normal unrelated female all their daughters must necessarily receive one haemophiliac X chromosome from the father and a normal X chromosome from the mother. The sons all receive a normal Y chromosome from the father and a normal X chromosome from the mother. They therefore do not suffer from the disease, nor can they transmit it to their offspring. But the daughters all have a haemophilac X chromosome, and they will necessarily transmit the disease to 50 per cent, of their sons after marriage with a normal male.


APPENDIX

OSSIFICATION TIMES

The ossification periods have been widely studied, but the work of Hess (i9 2 3)> although differing in some respects from that usually given in textbooks on osteology, is now recognized as being the most accurate series of observations at present available. These observations may be summarized as follows :

7th week : Mandible, diaphysis of clavicle.

8th week : Diaphysis of humerus, radius, and ulna. 9th week : The terminal phalanges, the 2nd and 3rd basal phalanges, and the 2nd and 3rd metacarpal bones of the hand ; the ilium ; the 2nd and 3rd metatarsals, and the terminal phalanges of the foot bones.

10th week : 1st rib, and the 4th and 1st basal phalanges of the hand.

10th to 12th week : 4th, 5th, and 1st metatarsals.


176 AIDS TO EMBRYOLOGY

nth to 1 2th week : The basal phalanx of the 5th digit, and the middle phalanges of the 2nd, 3rd, and 4th digits of the hand.

13th to 14th week : All the remaining metatarsals and the phalanges of the foot except the last phalanx of the 5th digit.

13th to 1 6th week : The middle phalanx of the 5th finger.

1 6th to 17th week : Descending ramus of ischium.

17th to 20th week : Odontoid process of axis.

2 1st to 24th week : Sternum.

2 1st to 28th week : Descending ramus of pubis.

2 1st to 29th week : Calcaneus (os calcis).

24th to 32nd week : Talus (astragalus).

33rd to 36th week : Last phalanx of the 5th digit of foot.

35th to 48th week : Distal epiphysis of femur, and occasionally the proximal epiphysis of tibia.

The wide variation in these figures might be accounted for by the statement of Pryor (1927), that ossification begins at an earlier date in female foetuses than in the male.



Historic Disclaimer - information about historic embryology pages 
Mark Hill.jpg
Pages where the terms "Historic" (textbooks, papers, people, recommendations) appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
   Aids to Embryology 1948: 1. Germ Cells | 2. Segmentation and Germ Layer Formation | 3. Changes in Female Genital Tract | 4. Implantation and Placentation | 5. Formation of the Embryo | 6. Skin and Accessory Structures | 7. Nervous System | 8. Special Sense | 9. Alimentary Canal | 10. Circulatory System | 11. Coelomic Cavities | 12. Urogenital System | 13. Muscular and Skeletal Systems | 14. Hereditary

Cite this page: Hill, M.A. (2024, April 26) Embryology Book - Aids to Embryology (1948) 14. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Aids_to_Embryology_(1948)_14

What Links Here?
© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G
Retrieved from ‘https://embryology.med.unsw.edu.au/embryology/index.php?title=Book_-_Aids_to_Embryology_(1948)_14&oldid=360731’
Powered by MediaWiki