Q.What is Sexual Reproduction? Describe the process of gamete formation in human males. OR Define Uni-parental Reproduction. Explain any three modes of asexual reproduction in the animal world.
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Start your 14-day free trial to unlock the full solution →Sexual reproduction involves fusion of male and female gametes; in human males, spermatogenesis in the testes produces haploid sperm through a well-defined sequence of cell divisions and maturation.
What is Sexual Reproduction?
Sexual reproduction is the mode of reproduction in which two parents (usually of opposite sex) are involved, producing gametes (sex cells) — a male gamete and a female gamete — which fuse together (fertilisation/syngamy) to form a zygote, which then develops into a new individual. It involves meiosis (to halve the chromosome number in gametes) and leads to genetic variation in the offspring, unlike asexual reproduction.
Gamete formation in human males (Spermatogenesis):
Spermatogenesis is the process of formation of haploid spermatozoa (sperm) from diploid germinal (spermatogonial) cells in the seminiferous tubules of the testes, and occurs as follows:
- Spermatogonia (diploid, 2n) present on the inside wall of the seminiferous tubules multiply by mitosis and increase in number.
- Some spermatogonia periodically undergo changes and enter meiosis to become primary spermatocytes (diploid, 2n).
- Each primary spermatocyte completes meiosis I to form two equal, haploid secondary spermatocytes (n).
- The secondary spermatocytes undergo meiosis II to produce four equal, haploid spermatids.
- Spermatids are then transformed into spermatozoa (sperm) by the process of spermiogenesis; the sperm heads become embedded in the Sertoli cells and are finally released from the seminiferous tubules by spermiation.
- This entire process is regulated by hormones: GnRH from the hypothalamus stimulates the pituitary to release LH (which stimulates Leydig cells to secrete testosterone) and FSH (which acts on Sertoli cells to help in spermiogenesis).
OR — Uni-parental reproduction and asexual modes in the animal world:
Uni-parental reproduction is reproduction involving only a single parent, without the formation and fusion of gametes — the offspring produced are (usually) genetically identical to the parent. Common asexual modes in the animal world include:
- Binary fission — the parent organism (e.g., Amoeba, Paramecium) divides into two equal daughter individuals.
- Budding — a small outgrowth (bud) forms on the parent body (e.g., Hydra) and eventually detaches to form a new individual. …
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