Question

Trace the events from copulation to zygote formation in a human female.

Answer 1

1. When coitus (copulation) occurs, the penis releases semen into the vagina (insemination).
2. The motile sperms travel quickly past the cervix, penetrate the uterus, and finally reach the fallopian tube's ampullary area.
3. The ovary's ovum is also transferred to the ampullary area, where fertilisation occurs.
4. Fertilisation can take place only if the ovum and sperms are transferred to the ampullary region at the same time. This is why not all copulations result in fertilisation and pregnancy.
5. The process of fusion of a sperm with an ovum is called fertilisation.
6. During fertilisation, a sperm comes into contact with the ovum's zona pellucida layer, causing alterations in the membrane that prevent further sperm from entering. As a result, only one sperm can fertilise an ovum.
7. The acrosome's secretions aid sperm entry into the cytoplasm of the ovum via the zona pellucida and plasma membrane.
8. This causes the secondary oocyte's meiotic division to be completed.
9. The second meiotic division is also uneven, producing a second polar body and a haploid ovum (ootid).
10. Soon, a diploid zygote is created when the haploid nuclei of the sperm and the ovum fuse together.