Q. 28

Schematically rep

Answer :

At Puberty



Figure. Schematically representation of spermatogenesis


• At puberty, in testis spermatogonia (the immature male germ cells) produce sperms by the process of spermatogenesis.


• On the inside wall of seminiferous tubules, the spermatogonia present.


• They are multiply by mitotic division and increase in numbers and each spermatogonium is diploid and contains 46 chromosomes.


Primary spermatocytes periodically undergo meiosis and complete the first meiotic division (reduction division).


• The first mitotic division leading to the formation of two equal haploid cells called secondary spermatocytes having only 23 chromosomes each.


• For the production of four equal haploid spermatids, the secondary spermatocytes undergo for the second mitotic division.


• Spermiogenesis is the process by which the spermatids are transformed into spermatozoa (sperms).


OR


1) Monoeciousflower characteristics as follows:


• The flowers are unisexual.


• Like maize and castor, both male and female flowers are present on the same plant.


• It allows geitonogamy but prevents autogamy.


2) Cleistogamous flowers characteristics as follows:


• Cleistogamous flowers do not open at all.


• The anthers and stigma present close to each other.


• When anthers dehisce in the flower buds, to effect pollination pollen grains comein contact with the stigma.


• It is autogamous as there is no chance of cross-pollen landing on the stigma.


3)self-incompatibility


• It is a genetic mechanism by which self- pollination does not take place.


4)Monoecious and cleistogamous flowers promote inbreeding.


Outbreeding is promoted by flower showing self-incompatibility.


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