write a essay influence of yolk one cleavage
Answers
Answered by
1
Yolk is always present in the egg at the beginning of cleavage in lesser (microlecithal egg) or greater (mesolecithal or macrolecithal egg) amounts. It remains evenly (isolecithal egg) or unevenly (Teleolecithal egg) distributed in the ooplasm of the eggs. The cell division (cleavage) occurs more rapidly in the active cytoplasm then the yolk laden cytoplasm of the egg.
The inert yolk granules or platelets behave entirely passively. Yolk exerts an intense preventing influence on the process of cleavage and the mechanics of moving the germ layers in their final positions. It delayed the process of mitosis, and even deters it from extending into the over dense regions. The amount of yolk influences the course of cleavage by the following ways:
(1) When heamount of stored yolk increases, the amount of active cytoplasm gradually decreases and the position of nucleus is variously affected. In Teleolecithal eggs (mesolecithal and polylecithal eggs), such displacement of zygotic nucleus from the geometrical centre of the egg to the less yolky cytoplasm is very common. The mitotic divisions of such a displaced nucleus result in unequal sized blastomeres.
(2) Every mitosis of cleavage involves movements of the cell components, the chromosomes, parts of cytoplasm constituting the achromatic figure the mitochondria, and the surface layer of the cell, the activity of which along the equator of the maternal cell leads to the eventual separation of the daughter cells.
The inert yolk granules or platelets behave entirely passively. Yolk exerts an intense preventing influence on the process of cleavage and the mechanics of moving the germ layers in their final positions. It delayed the process of mitosis, and even deters it from extending into the over dense regions. The amount of yolk influences the course of cleavage by the following ways:
(1) When heamount of stored yolk increases, the amount of active cytoplasm gradually decreases and the position of nucleus is variously affected. In Teleolecithal eggs (mesolecithal and polylecithal eggs), such displacement of zygotic nucleus from the geometrical centre of the egg to the less yolky cytoplasm is very common. The mitotic divisions of such a displaced nucleus result in unequal sized blastomeres.
(2) Every mitosis of cleavage involves movements of the cell components, the chromosomes, parts of cytoplasm constituting the achromatic figure the mitochondria, and the surface layer of the cell, the activity of which along the equator of the maternal cell leads to the eventual separation of the daughter cells.
Similar questions