Testes
Read the following passage carefully and answer the given questions.
The male reproductive system includes a pair of testes along with accessory ducts, glands and the external genitalia. In adults, each testis is oval, and has about 250 compartments called testicular lobules. Each lobule contains one to three highly coiled seminiferous tubules in which sperm is produced. Each seminiferous tubule is lined on its inner side by two types of cells called male germ cells (spermatogonia) and Sertoli cells. The male germ cells undergo meiotic divisions, finally leading to sperm formation, while Sertoli cells provide nutrition. The regions outside the seminiferous tubules called interstitial spaces, contain small blood vessels and interstitial cells or Leydig cells. The male sex accessory ducts include rete testis, vasa efferentia, epididymis and vas deferens. The male accessory glands include seminal vesicles, prostate and bulbourethral glands. Secretions of these glands constitute the seminal plasma and the secretions of bulbourethral glands also helps in the lubrication of the penis.
The ploidy and chromosome number of spermatogonia is respectively:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 2N and 46
The passage says that the male germ cells, the spermatogonia, line the seminiferous tubules and later undergo meiosis to form sperms. Spermatogonia are the starting cells of sperm formation and have the full set of chromosomes, so they are diploid (2N). In humans a diploid cell has 46 chromosomes. The chromosome number is halved only at meiosis I.
(1) N and 46 — Incorrect. N means haploid, and a haploid cell has 23 chromosomes. The two parts do not go together.
(2) 2N and 46 — Correct. A diploid cell with 46 chromosomes is a spermatogonium. The primary spermatocyte that forms from it also has 2N = 46.
(3) N and 23 — Incorrect. This is the number in the cells formed after meiosis: the secondary spermatocytes, the spermatids and the sperms.
(4) 2N and 23 — Incorrect. A diploid cell cannot have 23 chromosomes in humans. The two parts do not go together.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Gametogenesis – “… The spermatogonia (sing. spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonium is diploid and contains 46 chromosomes.”