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NCERT Exemplar · Q9

Q.The spermatogonia undergo division to produce sperms by the process of spermatogenesis. Choose the correct one with reference to above.

(a) Spermatogonia have 46 chromosomes and always undergo meiotic cell division
(b) Primary spermatocytes divide by mitotic cell division
(c) Secondary spermatocytes have 23 chromosomes and undergo second meiotic division
(d) Spermatozoa are transformed into spermatids
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Secondary spermatocytes contain 23 chromosomes (haploid) and complete spermatogenesis by undergoing the second meiotic division to form haploid spermatids.

Spermatogenesis is the process by which diploid spermatogonial stem cells in the seminiferous tubules of the testes transform into mature haploid spermatozoa. Understanding the chromosomal changes and the type of division at each stage is essential to grasp how genetic material is halved and gametes are formed.

The process begins with spermatogonia, which are diploid germ cells containing 46 chromosomes in humans. These cells do not "always" undergo meiosis. In fact, spermatogonia first undergo several rounds of mitotic divisions to maintain their population and produce more spermatogonia. Some of these then differentiate into primary spermatocytes, which marks the true beginning of meiosis. So option (A) is incorrect because spermatogonia undergo mitosis, not exclusively meiosis.

Primary spermatocytes are large diploid cells with 46 chromosomes. They enter meiosis I, not mitosis. During this first meiotic division, homologous chromosomes pair up, exchange genetic material through crossing over, and then separate. This reductional division produces two secondary spermatocytes, each now haploid with 23 chromosomes (though each chromosome still consists of two sister chromatids joined at the centromere). Option (B) is therefore wrong—primary spermatocytes divide by meiotic, not mitotic, division.

Important

The key reduction in chromosome number happens during meiosis I, when primary spermatocytes (46 chromosomes) divide to form secondary spermatocytes (23 chromosomes). …

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