Q. Which of the following represents reduction division during the process of spermatogenesis?
NTA AbhyasNTA Abhyas 2020
Solution:
In the testes, the immature male germ cells, spermatogonia produce sperms by process of spermatogenesis that begins at puberty.
Spermatogenesis occurs in four stages:
(i) Spermatocytogenesis: The process of spermatocytogenesis is divided into two phases- multiplication and growth phase.
- Multiplication Phase: In spermatocytogenesis, the spermatogonia present on the inside wall of the seminiferous tubules multiple by mitotic division and increase in number. Each spermatogonium is diploid containing 46 chromosomes.
- Growth Phase: Some spermatogonia undergo changes, they grow, increase in size by accumulating nourishing materials, and are called primary spermatocytes which periodically undergo meiosis and others remain as spermatogonia cells. Primary spermatocytes will remain in the testes and the whole maturation process takes place in the testes only.
(ii) Meiosis-I: A primary spermatocyte is diploid, (2n) with 44 + XY (total 46) chromosomes. It completes the first division (reduction division) leading to the formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each i.e. 22 + X or 22 + Y. During this time the chromosomes undergo synapsis, tetrad formation, and crossing over.
(iii) Meiosis-II: The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids. The number of chromosomes in each spermatid is 23.
Meiosis-I and Meiosis-II are together called as maturation phase.
(iv) Spermiogenesis: It is also known as the differentiation/transformation phase. The spermatids are transformed into spermatozoa (sperms) by the process of metamorphosis called Spermiogenesis. After spermatogenesis, the sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation. In spermatogenesis from one primary spermatocyte, four haploids are formed.
Spermatogenesis occurs in four stages:
(i) Spermatocytogenesis: The process of spermatocytogenesis is divided into two phases- multiplication and growth phase.
- Multiplication Phase: In spermatocytogenesis, the spermatogonia present on the inside wall of the seminiferous tubules multiple by mitotic division and increase in number. Each spermatogonium is diploid containing 46 chromosomes.
- Growth Phase: Some spermatogonia undergo changes, they grow, increase in size by accumulating nourishing materials, and are called primary spermatocytes which periodically undergo meiosis and others remain as spermatogonia cells. Primary spermatocytes will remain in the testes and the whole maturation process takes place in the testes only.
(ii) Meiosis-I: A primary spermatocyte is diploid, (2n) with 44 + XY (total 46) chromosomes. It completes the first division (reduction division) leading to the formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each i.e. 22 + X or 22 + Y. During this time the chromosomes undergo synapsis, tetrad formation, and crossing over.
(iii) Meiosis-II: The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids. The number of chromosomes in each spermatid is 23.
Meiosis-I and Meiosis-II are together called as maturation phase.
(iv) Spermiogenesis: It is also known as the differentiation/transformation phase. The spermatids are transformed into spermatozoa (sperms) by the process of metamorphosis called Spermiogenesis. After spermatogenesis, the sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by the process called spermiation. In spermatogenesis from one primary spermatocyte, four haploids are formed.