Question

$100$ spermatozoa and $100$ mature ova are formed by

• A. $50$ secondary spermatocytes and $50$ secondary oocytes
• B. $25$ secondary spermatocytes and $25$ secondary oocytes
• C. $25$ primary spermatocytes and $25$ primary oocytes
• D. $25$ primary spermatocytes and $100$ primary oocytes

Answer 1

Answer: (D)

$25$ primary spermatocytes and $100$ primary oocytes

Spermatogenesis is the process of formation of spermatid(n) from spermatogonia$\left(2n\right)$. The process goes as follows:-

Spermatogonia$\left(2n\right)⟶$ Primary Spermatocyte$\left(2n\right)⟶2$Secondary Spermatocyte$\left(n\right)⟶4$ Spermatid$\left(n\right)$

Oogenesis is the production of ovum from oogonia. The mechanism in short can be depicted as below:-

Oogonia$\left(2n\right)⟶$ Primary Oocyte$\left(2n\right)⟶$ Secondary Oocyte$\left(n\right)+$ Polar Body$\left(n\right)$

This meiosis $I$ is an unequal division leading to the formation of a haploid secondary oocyte and a polar body. The first polar body is said to be atretic and does not divide further. However, the secondary oocyte completes its meiosis during fertilization to form an ova(n) and the second polar body$\left(n\right)$.

So, for $100$ spermatozoa, we need $25$ primary spermatocytes and to produce $100$ mature ova, we need $100$ primary oocytes.

So the correct answer is D.