Cleavage (embryo)
Cleavage (embryo)
Cleavage in the context of Embryology refers to the division of cells in the early Embryo. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage, up to the Blastula stage, are called blastomeres.
Pronunciation
Cleavage: /ˈkliːvɪdʒ/
Etymology
The term "cleavage" is derived from the verb "cleave", which means to split or divide. In the context of embryology, it refers to the splitting or division of the embryo's cells.
Process
The process of cleavage begins after the fertilization of the egg by a sperm. The single-celled zygote begins to divide into multiple cells through a process called mitosis, resulting in a multicellular embryo. This process is crucial for the initial stages of embryonic development.
Types of Cleavage
There are two main types of cleavage: radial and spiral.
- Radial Cleavage: This type of cleavage is characteristic of deuterostomes, which include vertebrates and echinoderms. In radial cleavage, the cleavage planes are either parallel or perpendicular to the polar axis, resulting in blastomeres which are directly above or below each other.
- Spiral Cleavage: This type of cleavage is characteristic of protostomes, which include mollusks and annelids. In spiral cleavage, the cleavage planes are diagonal to the polar axis, resulting in blastomeres that are offset from each other.
Related Terms
External links
- Medical encyclopedia article on Cleavage (embryo)
- Wikipedia's article - Cleavage (embryo)
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