Schematically represent and explain the events of spermatogenesis in humans.

OR

Angiosperm flowers may be monoecious, cleistogamous or show self-incompatibility. Describe the characteristic features of each one of them and state which one of these flowers promotes inbreeding and outbreeding respectively.

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.