Describe the patterns and types of cleavage in detail?

Question: Describe the patterns and types of cleavage in detail?

 Cleavage is the process of cell division that occurs after fertilization, transforming the single-celled zygote into a multicellular embryo. The patterns and types of cleavage depend on the amount and distribution of yolk in the egg, which affects how the cleavage furrows divide the egg.

There are two main patterns of cleavage: holoblastic and meroblastic. Holoblastic cleavage occurs when the entire egg is divided into smaller cells, while meroblastic cleavage occurs when only a part of the egg is divided. Holoblastic cleavage can be further classified into equal, unequal, radial, bilateral, spiral or irregular, depending on the size and arrangement of the blastomeres. Meroblastic cleavage can be further classified into discoidal and superficial, depending on the location of the cleavage furrows.

There are also three main types of eggs based on yolk characteristics: isolecithal, mesolecithal and telolecithal. Isolecithal eggs have sparse and evenly distributed yolk, and undergo equal holoblastic cleavage. Mesolecithal eggs have moderate amount of yolk, often unevenly distributed, and undergo unequal holoblastic cleavage. Telolecithal eggs have dense yolk concentrated at one end, and undergo meroblastic cleavage.

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