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Human fertilization
Human Fertilization
Early Human Zygote

Fertilization is the fusion of haploid gametes, egg and sperm, to form the diploid zygote. Note though there can be subtle differences in the fertilization process which occurs naturally within the body or through reproductive technologies outside the body, the overall product in both cases is a diplod zygote. In fertilization research, after humans the mouse is the most studied species followed by domestic and farm animals. The process of fertilization involves components of, and signaling between, both sperm (spermatozoa) and egg (oocyte).

In addition to in vivo fertilization there are many new in vitro technologies related to human infertility (Assisted Reproductive Technology) and animal production somatic cell nuclear transfer (SCNT) to generate a zygote.

Note different spelling - USA spelling "fertilization", Australian spelling "fertilisation".

Fertilization Links: fertilization | oocyte | spermatozoa | meiosis | | ovary | testis | menstrual cycle | zona pellucida | zygote | granulosa cell Lecture - Fertilization | 2016 Lecture | mitosis | Lecture - Week 1 and 2 | hydatidiform mole | Assisted Reproductive Technology | | morula | blastocyst | Lecture - Genital Development | Category:Fertilization
Historic Embryology - Fertilization 
1910 Fertilization | 1919 Human Ovum | 1921 The Ovum | 1927 First polar body | 1929 Oocyte Size | 1943 Fertilization | 1944 In vitro fertilization | 1948 In vitro fertilization

Human-spermatozoa EM01.jpg

Some Recent Findings

  • Acrosin is essential for sperm penetration through the zona pellucida in hamsters PNAS February 4, 2020 117 (5) 2513-2518 "Mammalian oocytes are surrounded by the zona pellucida, a glycoprotein coat that protects the oocyte and embryo from mechanical damage during their preimplantation development within the oviduct. Fertilizing spermatozoa must penetrate the zona, but we do not know the exact mechanisms underlying this process. Sperm proteases were thought to work as zona lysins, but gene-knockout studies in mice did not support this assumption. In this study, we generated hamsters without acrosin, the major acrosomal protease, to examine its role in both in vivo and in vitro fertilization. Surprisingly, mutant male hamsters were completely infertile because their spermatozoa were unable to penetrate the zona. We thus demonstrated that, at least in hamsters, acrosin is essential for sperm penetration through the zona." OMIM - crosin
  • Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy[1] "During fertilization or chemically-induced egg activation, the mouse egg releases billions of zinc atoms in brief bursts known as 'zinc sparks.' The zona pellucida (ZP), a glycoprotein matrix surrounding the egg, is the first structure zinc ions encounter as they diffuse away from the plasma membrane. Following fertilization, the ZP undergoes changes described as 'hardening', which prevent multiple sperm from fertilizing the egg and thereby establish a block to polyspermy. A major event in zona hardening is cleavage of ZP2 proteins by ovastacin; however, the overall physiochemical changes contributing to zona hardening are not well understood. These results provide a paradigm-shifting model in which fertilization-induced zinc sparks contribute to the polyspermy block by altering conformations of the ZP matrix. This adds a previously unrecognized factor, namely zinc, to the process of ZP hardening."
More recent papers  
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References listed on the rest of the content page and the associated discussion page (listed under the publication year sub-headings) do include some editorial selection based upon both relevance and availability.

More? References | Discussion Page | Journal Searches | 2019 References | 2020 References

Search term: Fertilization | In vitro Fertilization | Polar Body

Older papers  
These papers originally appeared in the Some Recent Findings table, but as that list grew in length have now been shuffled down to this collapsible table.

See also the Discussion Page for other references listed by year and References on this current page.

  • Versatile action of picomolar gradients of progesterone on different sperm subpopulations[2] "High step concentrations of progesterone may stimulate various sperm physiological processes, such as priming and the acrosome reaction. However, approaching the egg, spermatozoa face increasing concentrations of the hormone, as it is secreted by the cumulus cells and then passively diffuses along the cumulus matrix and beyond. ... The results suggest a versatile role of the gradual distribution of very low doses of progesterone, which selectively stimulate the priming and the acrosome reaction in different sperm subpopulations."
  • Juno is the egg Izumo receptor and is essential for mammalian fertilization[3] "Fertilization occurs when sperm and egg recognize each other and fuse to form a new, genetically distinct organism. The molecular basis of sperm–egg recognition is unknown, but is likely to require interactions between receptor proteins displayed on their surface. Izumo1 is an essential sperm cell-surface protein, but its receptor on the egg has not been described. Here we identify folate receptor 4 (Folr4) as the receptor for Izumo1 on the mouse egg, and propose to rename it Juno. We show that the Izumo1–Juno interaction is conserved within several mammalian species, including humans. Female mice lacking Juno are infertile and Juno-deficient eggs do not fuse with normal sperm. Rapid shedding of Juno from the oolemma after fertilization suggests a mechanism for the membrane block to polyspermy, ensuring eggs normally fuse with just a single sperm."
  • Non-genetic contributions of the sperm nucleus to embryonic development[4] "Recent data from several laboratories have provided evidence that the newly fertilized oocyte inherits epigenetic signals from the sperm chromatin that are required for proper embryonic development. For the purposes of this review, the term epigenetic is used to describe all types of molecular information that are transmitted from the sperm cell to the embryo. There are at least six different forms of epigenetic information that have already been established as being required for proper embryogenesis in mammals or for which there is evidence that it may do so. These are (i) DNA methylation; (ii) sperm-specific histones, (iii) other chromatin-associated proteins; (iv) the perinuclear theca proteins; (v) sperm-born RNAs and, the focus of this review; and (vi) the DNA loop domain organization by the sperm nuclear matrix. These epigenetic signals should be considered when designing protocols for the manipulation and cryopreservation of spermatozoa for assisted reproductive technology as necessary components for effective fertilization and subsequent embryo development."
  • CD9 tetraspanin generates fusion competent sites on the egg membrane for mammalian fertilization[5] "CD9 tetraspanin is the only egg membrane protein known to be essential for fertilization. To investigate its role, we have measured, on a unique acrosome reacted sperm brought in contact with an egg, the adhesion probability and strength with a sensitivity of a single molecule attachment. Probing the binding events at different locations of wild-type egg we described different modes of interaction. Here, we show that more gamete adhesion events occur on Cd9 null eggs but that the strongest interaction mode disappears. We propose that sperm-egg fusion is a direct consequence of CD9 controlled sperm-egg adhesion properties. CD9 generates adhesion sites responsible for the strongest of the observed gamete interaction. These strong adhesion sites impose, during the whole interaction lifetime, a tight proximity of the gamete membranes, which is a requirement for fusion to take place. The CD9-induced adhesion sites would be the actual location where fusion occurs."
  • Gamete recognition in mice depends on the cleavage status of an egg's zona pellucida protein[6] "sperm-egg recognition depends on the cleavage status of ZP2 and that binding at the surface of the zona is not sufficient to induce sperm acrosome exocytosis."


The first polar body deforms the mammalian egg away from its encapsulating zona pellucida
  • Understand the mechanisms of gamete formation.
  • Understand the mechanisms of cell division.
  • Describe the differences between mitosis and meiosis.
  • Understand the mechanisms of fertilization, both in vivo and in vitro.
  • Describe the cleavage of the zygote.
  • Have a preliminary understanding of the role and process in male sex determination and X inactivation.
  • Understand the abnormalities that occur during this period of development.


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 ‎‎Spermatozoa Motility
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 ‎‎Fertilisation to
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 ‎‎Mouse Fertilisation
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 ‎‎Week 1
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Fertilization Preparation

Prior to the fertilization process commencing both the gametes oocyte (egg) and spermatozoa (sperm) require completion of a number of biological processes.

  • Oocyte meiosis - completes Meiosis 1 and commences Meiosis 2 (arrests at Metaphase II).
  • Spermatozoa Capacitation - following release (ejaculation) and mixing with other glandular secretions, activates motility and acrosome preparation.
  • Migration - both oocyte and spermatozoa.
    • oocyte ovulation and release with associated cells, from ovary into fimbria then into uterine tube (oviduct, uterine horn, fallopian tube) and epithelial cilia mediated movement.
    • spermatozoa ejaculation, deposited in vagina, movement of tail to "swim" in uterine secretions through cervix, uterine body and into uterine tube, have approximately 24-72h to fertilize oocyte.

Endocrinology - Diagram of the comparative anatomy of the male and female reproductive tracts


Histology of the Ovary
Preantral Follicle
Antral Follicle and Oocyte
  • Process of oogonia mature into oocytes (ova, ovum, egg)
  • all oogonia form primary oocytes before birth, therefore a maturation of preexisting cells in the female gonad, ovary

Human ovary non-growing follicle model.jpg

  • humans usually only 1 ovum released every menstrual cycle (IVF- superovulation)
  • oocyte and its surrounding cells = follicle
  • primary -> secondary -> ovulation releases

Ovary- Histology - whole transverse section (cortex, medulla)

Menstrual Cycle

  • Primary Oocyte - arrested at early Meiosis 1
    • diploid: 22 chromosome pairs + 1 pair X chromosomes (46, XX)
    • autosomes and sex chromosome
  • Oogenesis- pre-antral then antral follicle (Graafian follicle is mature antral follicle released)
  • Secondary oocyte
    • 1 Day before ovulation completes (stim by LH) Meiosis 1
    • haploid: 22 chromosomes + 1 X chromosome (23, X)
    • nondisjunction- abnormal chromosome segregation
    • begins Meiosis 2 and arrests at metaphase
    • note no interphase replication of DNA, only fertilization will complete Meiosis 2

Ovulation (HPG Axis)

Menstrual cycle.png

  • Hypothalmus releases gonadotropin releasing hormone (GRH, luteinizing hormone–releasing hormone, LHRH) -> Pituitary releases follicle stimulating hormone (FSH) and lutenizing hormone (LH) -> ovary follicle development and ovulation.
    • release of the secondary oocyte and formation of corpus luteum
    • secondary oocyte encased in zona pellucida and corona radiata
  • Ovulation associated with follicle rupture and ampulla movement.

Zona Pellucida

Mouse zona pellucida[7]

zona pellucida glycoprotein shell ZP1, ZP2, ZP3, ZP4 (mouse only ZP1-3)

  1. mechanical protection of egg
  2. involved in the fertilization process
  3. sperm binding
  4. adhesion of sperm to egg
  5. acrosome reaction
  6. releases enzymes to locally breakdown
  7. cortical granules modify to block of polyspermy
  8. altered to prevent more than 1 sperm penetrating
  9. mechanical protection of zygote, blastomeres, morula and blastocyst
  10. role in development of the blastocyst

Links: zona pellucida | MBoC - Figure 20-21. The zona pellucida

Corona Radiata

Mouse granulosa cells
Mouse granulosa cells[8]
  • granulosa cells and extracellular matrix
  • protective and nutritional role for cells during transport
  • cells are also lost during transport along oviduct


  • process of spermatagonia mature into spermatozoa (sperm)
  • continuously throughout life occurs in the seminiferous tubules in the male gonad- testis (plural testes)
  • at puberty spermatagonia activate and proliferate (mitosis)
  • primary spermatocyte -> secondary spermatocyte-> spermatid->sperm
  • Seminiferous Tubule is site of maturation involving meiosis and spermiogenesis
  • Spermatogenesis- Meiosis
  • meiosis is reductive cell division
    • 1 spermatagonia (diploid) 46, XY (also written 44+XY) = 4 sperm (haploid); 23, X 23, X 23, Y 23, Y


  • morphological (shape) change from round spermatids to elongated sperm
  • loose cytoplasm
  • Transform golgi apparatus into acrosome (in head)
  • Organize microtubules for motility (in tail, flagellum)
  • Segregate mitochondria for energy (in tail)

Links: spermatozoa


  • Human Ejaculate
    • By volume <10 % sperm and accessory glands contribute majority of volume (60 % seminal vesicle, 10 % bulbourethral, 30 % prostate)
    • 3.5 ml, 200-600 million sperm.
  • Capacitation is the removal of glycoprotein coat and seminal proteins and alteration of sperm mitochondria.
  • Ovulation-inducing factor identified in several species.[9]
  • Infertility can be due to Oligospermia, Azoospermia, Immotile Cilia Syndrome
    • Oligospermia (Low Sperm Count) - less than 20 million sperm after 72 hour abstinence from sex
    • Azoospermia (Absent Sperm) - blockage of duct network
    • Immotile Cilia Syndrome - lack of sperm motility

Links: spermatozoa | prostate

Fertility Window

Probability of women with regular or irregular cycles being in their fertile window

Clinical guidelines have typically identified the "fertile window" between days 10 and 17 within the typical 28 day menstrual cycle.

Data from a large USA NIEHS - Early Pregnancy Study (1982-86) identified the timing of the “fertile window” within a range of different menstrual cycles.[10]

  • fertile window occurred during a broad range of days in the menstrual cycle.
  • between days 6 and 21 women had at minimum a 10% probability of being in their fertile window.
  • women cannot predict a sporadic late ovulation; 4 - 6% of women whose cycles had not yet resumed were potentially fertile in the fifth week of their cycle.
  • only about 30% of women is the fertile window entirely within the days of the menstrual cycle identified by clinical guidelines (between days 10 and 17)
  • most women reach their fertile window earlier and others much later.
  • women should be advised that the timing of their fertile window can be highly unpredictable, even if their cycles are usually regular.
Links: menstrual cycle

Fertilization Site

Week 1
  • Fertilization usually occurs in first 1/3 of oviduct
  • Fertilization can also occur outside oviduct, associated with In Vitro Fertilization (IVF, GIFT, ZIFT...) and ectopic pregnancy
  • The majority of fertilized eggs do not go on to form an embryo

Fertilization - Spermatozoa

  • Contact between spermatozoa and oocyte egg coat (zona pellucida [ZP]) glycoproteins triggers increases in intracellular calcium ion (iCa2+) concentration in spermatozoa[11]
  • CATSPER channels on the distal portion of sperm (the principal piece) are required for the ZP-induced iCa2+ increases
  • iCa2+ increase starts from the spermatozoa tail and propagates toward the head
  • Store depletion-activated Ca2+ entry is thought to mediate the sustained phase

Fertilization - Oocyte

Spermatozoa - Oocyte Interaction

Membrane Fusion

Spermatozoa and oocyte fusion in the membrane adhesion area requires the presence of 3 membrane proteins (spermatozoa Izumo1; oocyte receptor Juno and Cd9).[12]


The sperm-specific protein Izumo is named for a Japanese shrine dedicated to marriage and is essential for sperm-egg plasma membrane binding and fusion. It interacts with the spermatozoa folate receptor 4 (Folr4).

Links: OMIM 609278


folate receptor 4 (Folr4)

Folate receptors are also known as the folic acid (FA) binding protein and bind of 5-methyltetrahydrofolate (5-MeTHF).


Oocyte cell surface protein acts as a receptor for pregnancy-specific glycoprotein 17 (Psg17).

Links: OMIM 143030


(Astacin-Like Metalloendopeptidase, ASTL) An oocyte enzyme (zinc-dependent metalloprotease) involved in altering zona pellucida structure, by cleaving zona pellucida glycoprotein (ZP2), following fertilisation.[13] This change in zona pellucida structure is one of the blockers to polyspermy.
Mouse oocyte cortical granule (green) ovastacin (red) staining.[13]

Formation of the Zygote

Early human zygote showing Pronuclei
  • Pronuclei - Male and Female haploid nuclei approach each other and nuclear membranes break down
  • chromosomal pairing, DNA replicates, first mitotic division
  • Spermatozoa contributes - centriole which organizes mitotic spindle
  • Oocyte contributes - mitochondria (maternally inherited)


  • Mitochondria of the spermatozoa are specifically destroyed in early development by proteolysis (mouse 4 to 8 cell transition).[14]
  • Metaphase II oocytes in rats have an average mitochondrial DNA (mtDNA) copy number of 147,600 (+/-3000) that only increases at the 8-cell stage.[15]

Sex Determination

  • based upon whether an X or Y carrying sperm has fertilized the egg, should be 1.0 sex ratio.
  • actually 1.05, 105 males for every 100 females, some studies show more males 2+ days after ovulation.
  • cell totipotent (equivalent to a stem cell, can form any tissue of the body)

Men - Y Chromosome

  • Y Chromosome carries Sry gene, protein product activates pathway for male gonad (covered in genital development)

Women - X Chromosome

  • Gene dosage, one {ChrX}} chromosome in each female embryo cell has to be inactivated
  • process is apparently random and therefore 50% of cells have father's X, 50% have mother's X
  • Note that because men only have 1 X chromosome, if abnormal, this leads to X-linked diseases more common in male that female where bothe X's need to be abnormal.

Fertilization Protein Changes

A recent study in mice has shown that after fertilization the maternal proteins present in the original oocyte are quickly degraded by the zygote stage. MII oocytes have 185,643 different peptides while zygotes contain only 85,369 peptides.[16]

Protein Expression Classified by Molecular Functions

MII oocyte
Mouse- MII oocyte protein expression.jpg Mouse- zygote protein expression.jpg


The abnormalities listed below relate to genetic abnormalities resulting in infertility or occurring during fertilisation. There are of course many additional genetic abnormalities inherited and introduced by the recombined maternal and paternal genomes, other than trisomy 21 these will not be covered here. Note the sex different genes responsible shown for the examples of male and female infertility.

Male Infertility Genes

Selected genes in Male Infertility
Gene abbreviation Name Gene Location Online Mendelian
Inheritance in Man (OMIM)
HUGO Gene Nomenclature
Committee (HGNC)
GeneCards (GCID) Diagnosis
AURKC Aurora kinase C 19q13.43 603495 11391 GC19P057230 Macrozoospermia
CATSPER1 Cation channel sperm-associated 1 11q13.1 606389 17116 GC11M066034 Asthenozoospermia
CFTR Cystic fibrosis transmembrane conductance regulator 7q31.2 602421 1884 GC07P117465 Obstructive azoospermia
DNAH1 Dynein axonemal heavy chain 1 3p21.1 603332 2940 GC03P052350 Asthenozoospermia
DPY19L2 Dpy-19-like 2 gene 12q14.2 613893 19414 GC12M063558 Globozoospermia
GALNTL5 Polypeptide N-acetylgalactosaminyltransferase-like 5 7q36.1 615133 21725 GC07P151956 Asthenozoospermia
MAGEB4 MAGE family member B4 Xp21.2 300153 6811 GC0XP030260 Azoospermia
NANOS1 Nanos C2HC-type zinc finger 1 10q26.11 608226 23044 GC10P119029 Azoospermia
NR0B1 Nuclear receptor subfamily 0 group B member 1 Xp21.2 300473 7960 GC0XM030322 Azoospermia
NR5A1 Nuclear receptor subfamily 5 group A member 1 9q33.3 184757 7983 GC09M124481 Azoospermia
SOHLH1 Spermatogenesis and oogenesis-specific basic helix–loop–helix 1 9q34.3 610224 27845 C09M135693 Azoospermia
vSPATA16 Spermatogenesis-associated 16 3q26.31 609856 29935 GC03M172889 Globozoospermia
SYCE1 Synaptonemal complex central element protein 1 10q26.3 611486 28852 GC10M133553 Azoospermia
TAF4B TATA-box binding protein-associated factor 4b 18q11.2 601689 11538 GC18P026225 Azoospermia
TEX11 Testis expressed 11 Xq13.1 300311 11733 GC0XM070528 Azoospermia
TEX15 Testis expressed 15, meiosis and synapsis associated 8p12 605795 11738 GC08M030808 Azoospermia
WT1 Wilms tumour 1 8p12 607102 12796 GC11M032365 Azoospermia
ZMYND15 Zinc-finger MYND-type containing 15 17p13.2 614312 20997 GC17P004740 Azoospermia
  Table data source[17] (table 1)    Links: fertilization | spermatozoa | testis | Male Infertility Genes | Female Infertility Genes | oocyte | ovary | Genetic Abnormalities | ART

  Asthenozoospermia - (asthenospermia) term for reduced spermatozoa motility. Azoospermia - term for no spermatozoa located in the ejaculate. Globozoospermia - term for spermatozoa with a round head and no acrosome.

Female Infertility Genes

Selected Female Infertility Genes
Gene abbreviation Name Gene Location Online Mendelian
Inheritance in Man (OMIM)
HUGO Gene Nomenclature
Committee (HGNC)
GeneCards (GCID) Diagnosis
BMP15 Bone morphogenetic protein 15 Xp11.22 300247 1068 GC0XP050910 Primary ovarian insufficiency
CLPP Caseinolytic mitochondrial matrix peptidase proteolytic subunit 19p13.3 601119 2084 GC19P006369 Primary ovarian insufficiency
EIF2B2 Eukaryotic translation initiation factor 2B subunit beta 14q24.3 606454 3258 GC14P075002 Primary ovarian insufficiency
FIGLA Folliculogenesis-specific BHLH transcription factor 2p13.3 608697 24669 GC02M070741 Primary ovarian insufficiency
FMR1 Fragile X mental retardation 1 Xq27.3 309550 3775 GC0XP147912 Primary ovarian insufficiency
FOXL2 Forkhead box L2 3q22.3 605597 1092 GC03M138944 Primary ovarian insufficiency
FSHR Follicle stimulating hormone receptor 2p16.3 136435 3969 GC02M048866 Primary ovarian insufficiency
GALT Galactose-1-phosphate uridylyltransferase 9p13.3 606999 4135 GC09P034636 Primary ovarian insufficiency
GFD9 Growth differentiation factor 9 5q31.1 601918 4224 GC05M132861 Primary ovarian insufficiency
HARS2 Histidyl-TRNA synthetase 2, mitochondrial 5q31.3 600783 4817 GC05P141975 Primary ovarian insufficiency
HFM1 HFM1, ATP-dependent DNA helicase homolog 1p22.2 615684 20193 GC01M091260 Primary ovarian insufficiency
HSD17B4 Hydroxysteroid 17-beta dehydrogenase 4 5q23.1 601860 5213 GC05P119452 Primary ovarian insufficiency
LARS2 Leucyl-TRNA synthetase 2, mitochondrial 3p21.31 604544 17095 GC03P045405 Primary ovarian insufficiency
LHCGR Luteinizing hormone/choriogonadotropin receptor 2p16.3 152790 6585 GC02M048647 Primary ovarian insufficiency
LHX8 LIM homeobox 8 1p31.1 604425 28838 GC01P075128 Primary ovarian insufficiency
MCM8 Minichromosome maintenance 8 homologous recombination repair factor 20p12.3 608187 16147 GC20P005926 Primary ovarian insufficiency
MCM9 Minichromosome maintenance 9 homologous recombination repair factor 6q22.31 610098 21484 GC06M118813 Primary ovarian insufficiency
NOBOX NOBOX oogenesis homeobox 7q35 610934 22448 GC07M144397 Primary ovarian insufficiency
NOG Noggin 17q22 602991 7866 GC17P056593 Primary ovarian insufficiency
PMM2 Phosphomannomutase 2 16p13.2 601785 9115 GC16P008788 Primary ovarian insufficiency
POLG DNA polymerase gamma, catalytic subunit 15q26.1 174763 9179 GC15M089316 Primary ovarian insufficiency
REC8 REC8 meiotic recombination protein 14q12 608193 16879 GC14P024171 Primary ovarian insufficiency
SMC1B Structural maintenance of chromosomes 1B 22q13.31 608685 11112 GC22M045344 Primary ovarian insufficiency
SOHLH1 Spermatogenesis and oogenesis-specific basic helix–loop–helix 1 9q34.3 610224 27845 GC09M135693 Primary ovarian insufficiency
STAG3 Stromal antigen 3 7q22.1 {{Chr 608489 11356 GC07P100177 Primary ovarian insufficiency
SYCE1 Synaptonemal Complex Central Element Protein 1 10q26.3 611486 28852 GC10M133553 Primary ovarian insufficiency
TLE6 Transducin-like enhancer of split 6 19p13.3 612399 30788 GC19P002976 Embryonic lethalithy
TUBB8 Tubulin beta 8 Class VIII 10p15.3 616768 20773 GC10M000048 Oocyte maturation arrest
TWNK Twinkle MtDNA helicase 10q24.31 606075 1160 GC10P100991 Primary ovarian insufficiency
  Table data source[17] (table 1)    Links: fertilization | oocyte | ovary | | Female Infertility Genes | spermatozoa | testis | Male Infertility Genes | Genetic Abnormalities | ART

 Primary ovarian insufficiency - depletion or dysfunction of ovarian follicles with cessation of menses before age 40 years.
 Oocyte maturation arrest - arrest of human oocytes may occur at different stages of meiosis.

Complete Hydatidiform Mole

  • Chromosomal genetic material from the oocyte (ovum, egg) is lost, by an unknown process.
  • Fertilization then occurs with one or two spermatozoa and an androgenic (from the male only) conceptus (fertilized oocyte) is formed.
  • The embryo (fetus, baby) does not develop at all but the placenta does grow.
Links: hydatidiform mole

Partial Hydatidiform Mole

Three sets of chromosomes instead of the usual two and this is called triploidy.

  • chromosomal (genetic) material from the oocyte (ovum, egg) is retained and the egg is fertilized by one or two spermatozoa.
  • with partial mole there are maternal chromosomes and there is a fetus.
  • the three sets of chromosomes means the fetus is always grossly abnormal and will not survive.
Links: hydatidiform mole


(Greek, parthenos = virgin, genesis = birth) The development of an unfertilized oocyte (no spermatozoa). Other than mammals, many different species (plants, insects, reptiles) can develop from unfertilized eggs. An embryo so formed without sperm contribution. Blocking of parthenogenesis in mammals appears to be related to genomic imprinting. Abnormal parthenogenic processes can occur in mammals, and more recently a parthenogenic mouse has been made in the laboratory.

Trisomy 21

Trisomy 21 (Down's or Down syndrome) is caused by nondisjunction of chromosome 21 in a parent who is chromosomally normal and is one of the most common chromosomal aneuploidy abnormalities in liveborn children. The frequency of trisomy 21 in the population is approximately 1 in 650 to 1,000 live births, in Australia between 1991-97 there were 2,358 Trisomy 21 infants. There are other less frequently occurring trisomies (Trisomy 18, Trisomy 13 and Trisomy X).

Links: Trisomy 21


  1. Que EL, Duncan FE, Bayer AR, Philips SJ, Roth EW, Bleher R, Gleber SC, Vogt S, Woodruff TK & O'Halloran TV. (2017). Zinc sparks induce physiochemical changes in the egg zona pellucida that prevent polyspermy. Integr Biol (Camb) , 9, 135-144. PMID: 28102396 DOI.
  2. Uñates DR, Guidobaldi HA, Gatica LV, Cubilla MA, Teves ME, Moreno A & Giojalas LC. (2014). Versatile action of picomolar gradients of progesterone on different sperm subpopulations. PLoS ONE , 9, e91181. PMID: 24614230 DOI.
  3. Bianchi E, Doe B, Goulding D & Wright GJ. (2014). Juno is the egg Izumo receptor and is essential for mammalian fertilization. Nature , 508, 483-7. PMID: 24739963 DOI.
  4. Yamauchi Y, Shaman JA & Ward WS. (2011). Non-genetic contributions of the sperm nucleus to embryonic development. Asian J. Androl. , 13, 31-5. PMID: 20953203 DOI.
  5. Jégou A, Ziyyat A, Barraud-Lange V, Perez E, Wolf JP, Pincet F & Gourier C. (2011). CD9 tetraspanin generates fusion competent sites on the egg membrane for mammalian fertilization. Proc. Natl. Acad. Sci. U.S.A. , 108, 10946-51. PMID: 21690351 DOI.
  6. Gahlay G, Gauthier L, Baibakov B, Epifano O & Dean J. (2010). Gamete recognition in mice depends on the cleavage status of an egg's zona pellucida protein. Science , 329, 216-9. PMID: 20616279 DOI.
  7. Wassarman PM. (2008). Zona pellucida glycoproteins. J. Biol. Chem. , 283, 24285-9. PMID: 18539589 DOI.
  8. Zhou HX, Ma YZ, Liu YL, Chen Y, Zhou CJ, Wu SN, Shen JP & Liang CG. (2014). Assessment of mouse germinal vesicle stage oocyte quality by evaluating the cumulus layer, zona pellucida, and perivitelline space. PLoS ONE , 9, e105812. PMID: 25144310 DOI.
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Mou L & Xie N. (2017). Male infertility-related molecules involved in sperm-oocyte fusion. J. Reprod. Dev. , 63, 1-7. PMID: 27904014 DOI.


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Duncan FE, Que EL, Zhang N, Feinberg EC, O'Halloran TV & Woodruff TK. (2016). The zinc spark is an inorganic signature of human egg activation. Sci Rep , 6, 24737. PMID: 27113677 DOI.

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