Question

Which of the following is/are responsible for the formation of the ootid?

• A. The fusion of male and female pronuclei
• B. The entry of the sperm into the cytoplasm of the primary oocyte
• C. The release of cortical vesicles outside the plasma membrane of the oocyte
• D. The entry of the sperm into the cytoplasm of the secondary oocyte

Answer 1

The correct option is D The entry of the sperm into the cytoplasm of the secondary oocyte

After the successful entry of the sperm into the cytoplasm of the secondary oocyte, the oocyte which was suspended at metaphase of meiosis II, proceeds further and completes its meiotic division. This gives rise to an ovum or ootid and a second polar body.

After the formation of the ovum, the nuclear material within the ovum reorganises into the female pronuclei. The nucleus of the spermatozoa also swells up as it forms the male pronucleus. The two pronuclei fuse in a process called amphimixis.

The release of cortical vesicles outside the plasma membrane of the oocyte leads to cortical reactions which help in the prevention of polyspermy.