→ The process of fusion of a sperm with an ovum is called fertilisation.
→ During fertilisation, a sperm comes in contact with the zona pellucida layer of the ovum and induces changes in the membrane that block the entry of additional sperms. Thus, it ensures that only one sperm can fertilise an ovum.
→ The secretions of the acrosome help the sperm enter into the cytoplasm of the ovum through the zona pellucida and the plasma membrane. This induces the completion of the meiotic division of the secondary oocyte.
→ The second meiotic division is also unequal and results in the formation of a second polar body and a haploid ovum (ootid).
→ Soon the haploid nucleus of the sperms and that of the ovum fuse together to form a diploid zygote.