- Fusion of sperm nucleus with egg nucleus to form a diploid zygote cell
- Occurs in upper parts of fallopian tube ie. Ampulla
Process of Fertilization
1. Ejaculation in vagina
2. Capacitation – removal of glycoproteins to make sperm active and identify ovum
3. 1st contact – Acrosome reaction
- Contact of head of sperm with zona granulosa cells
- Acrosome reaction – Acrosome burst by exocytosis
- Releases hydrolytic enzymes
4. Break down of first barrier – Corona radiata
- Enzymes digest the sticky substances that holds the follicle cells together
- Cause cells to break away from zona pellucida
5. Break down of 2nd barrier – Zona pellucida
- Another acrosomal enzyme then digests the zona pellucida to create path for entry of the sperm cell
6. Contact with third barrier – Oocyte membrane
Formation of fertilization membrane:
- Head of 1st sperm makes contact with oocyte membrane
- Oocyte membrane become permeable to calcium ions
- Calcium ions rush into oocyte by diffusion
- Calcium ions stimulate rapid exocytosis of cortical granules, which release chemical substances
- Cortical reaction – release of cortical granules
- A new membrane forms, called fertilization membrane
- Fertilization membrane prevents polyspermy (entry of many sperm cells)
Q) How does fertilization membrane prevent polyspermy?
Acrosomal enzymes released by other sperms cannot digest the changed zona pellucida/fertilization membrane
7. Release of sperm nucleus into the secondary oocyte
8. This stimulates 2ry oocyte to complete 2nd meiotic division and form a true ovum
9. Fusion of male and female pronucleus (enlarged nucleus) to form a zygote