Q.Given below is a diagrammatic sectional view of a seminiferous tubule. State the developmental process of : [Figure: sectional view of seminiferous tubule with labels a, b, c, d, e]
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Start your 14-day free trial to unlock the full solution →The seminiferous tubule houses spermatogenesis: spermatogonia (a) divide mitotically to form primary spermatocytes (b), which undergo meiosis I to produce secondary spermatocytes (d), then meiosis II to yield spermatids (e), which finally differentiate into spermatozoa through spermiogenesis.
The seminiferous tubule is the functional unit of the testis where sperm production unfolds in a beautifully orchestrated sequence. Arranged in concentric layers from the basement membrane toward the lumen, germ cells at different stages of development sit nestled among Sertoli cells, which nourish and support them. Understanding this spatial arrangement is key to deciphering the developmental cascade.
At the outermost layer, against the basement membrane, lie the spermatogonia—diploid stem cells that serve as the starting point. These cells undergo mitotic divisions throughout reproductive life, ensuring a continuous supply of cells for sperm production while also maintaining their own population through self-renewal.
(a) The Developmental Processes
- Development of 'b' from 'a' Spermatogonia (a) undergo mitotic division to produce primary spermatocytes (b). Some spermatogonia differentiate and grow in size, accumulating cytoplasm and duplicating their DNA. This growth phase transforms them into larger, diploid primary spermatocytes, which then move slightly inward from the basement membrane. This mitotic proliferation ensures that the pool of germ cells is constantly replenished.
- Development of 'e' from 'd' Secondary spermatocytes (d) undergo the second meiotic division—meiosis II—to form spermatids (e). This division is equational, meaning the cells divide without further DNA replication. Each secondary spermatocyte, which is haploid but still has sister chromatids joined at the centromere, splits to produce two haploid spermatids. These spermatids are small, round cells with a haploid nucleus, positioned closer to the lumen of the tubule.
- Development of 'd' from 'b'
Primary spermatocytes (b) undergo the first meiotic division—meiosis I—to produce secondary spermatocytes (d). This is the reductional division where homologous chromosomes separate, reducing the chromosome number from diploid to haploid. Each primary spermatocyte yields two secondary spermatocytes, which are short-lived and quickly proceed to the next division. Meiosis I is crucial because it introduces genetic variation through crossing over and independent assortment.
Note
Secondary spermatocytes have a very brief existence in the seminiferous tubule—they rapidly enter meiosis II, which is why they are often difficult to spot in histological sections compared to the more abundant primary spermatocytes and spermatids.
(b) Identification of Cells
- 'a' – Spermatogonia: These are the diploid germ cells located at the periphery, against the basement membrane. They are the stem cells of spermatogenesis, undergoing mitosis to maintain their population and to produce cells that will differentiate further. …
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