The nuclear genetic factors, or genes, remaining dormant throughout the period of cleavage, begin to manifest themselves during gastrulation, and in ever-increasing measure control the process of development from this stage onward. This does not mean that the process taking place during cleavage are not affected by genes but the effect of the genes is [...]
The gastrulation is the most active phase of embryonic development during which extensive or profound morphogenetic activities of different types of blastomeres occur and rate of metabolism of gastrula as a whole becomes rapidly increased. Its metabolism can be studied under following headings:
(a) Catabolism- The morphogenetic movements during gastrulation cause an increased expenditure of energy [...]
Gastrulation is a nicely integrated, dynamic process one, which is controlled largely by intrinsic forces bound up in the specific physicho-chemical conditions of the various presumptive organ forming areas of the late blastula and early gastrula. These internal forces in turn are correlated with external conditions. In most vertebrates, it includes different kinds of morphogenetic [...]
The correct interpretation of gastrulation is impossible without a knowledge of the position which the presumptive germinal layers occupy in the blastula. This position may be ascertained in various ways. A chart showing the fate of each part of an early embryo, in a particular blastula, is called fate map. The fate maps of different [...]
In the blastula, most of the blastomeres which have to become differentiated into the cells of three fundamental germinal layers- ectoderm, endoderm and mesoderm of the future embryo, occur in a single layered blastoderm and at the external surface of the blastula. To occupy their respective positions in the embryo the blastomeres of presumptive organ [...]
The cleavage occurs more readily in the active cytoplasm than the yolk-laden cytoplasm or deutoplasm of the egg. The yolk which occurs in all animal eggs in little (e.g., microlecithal eggs) or larger (e.g., mesolecithal and macrolecithal eggs) amounts and remains distributed evenly (e.g., isolecithal eggs) or unevenly (e.g., telolecithal eggs) in the ooplasm of [...]
The cleavage is a phase of intensified chemical activity and a great amount of turn over of molecules occurs during its metabolism. The metabolism of cleavage can be studied under following two headings:
A. Catabolic activities of cleavage- The cleavage requires large amount of chemical energy in the form of ATP molecules for its completion. For [...]
