![]() ![]() Meroblastic superficial : This cleavage results in a superficial layer of blastomeres around the central yolk e.g.g., centrolecithal eggs of insects.įig.Meroblastic discoidal : The division is restricted to animal pole side resulting in only plate like structure e.g., In polylecithal eggs of reptiles and birds. ![]() The cleavage furrow in macrolecithal egg does not divide the zygote completely and is restricted to only animal pole. Hence, the blastomeres on this side are bigger (macromeres) and on animal pole side are smaller (micromeres). Holoblastic unequal : On equatorial plane blastomeres are divided unequally due to higher amount of yolk on vegetal side. Holoblastic equal : The blastomeres are divided equally in size, occurs in isolecithal (or microlecithal) eggs. The cleavage furrow divides the zygote (or blastomere) completely. This primarily depends upon the type of egg The synchrony of division is maintained upto 64 cell stage. The first cleavage furrow appears at animal-vegetal axis (meridional)Ģ nd division is also meridional but at right angle to the first one forming four blastomeres.ģ rd division is equatorial resulting into eight blastomeres.Ĥ th furrow is again meridional forming 16 cell stage called morula.ĥ th furrow is equatorial though this may differ in different animals. The rate of division depends upon the species (of animal) and the temperature. O 2 consumption is very high for high rate of metabolism. Rapid division is complemented by very fast DNA synthesis, but in human cleavage divisions are slowest in the animal kingdom. The nucleo-cytoplasmic ratio of the resultant cell after every division increases.Įarly few division in all blastomeres are synchronous (except in human). It is the mitotic cell division in zygote with following special features :Ĭell division without growth phase hence the cell number increases but size of embryo remains the same as that of zygote. Formation of embryo from zygote includes following stages : ![]()
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