What happens during cleavage after fertilization?

Cleavage is the initial phase of embryological development following fertilization, characterized by a series of rapid mitotic cell divisions that transform the single-celled zygote into a multicellular structure.12

Key aspects of this process include:

• Cellular Division: The zygote divides into smaller cells called blastomeres. Because there is little to no growth between these divisions, the total volume of the embryo remains roughly the same as the original zygote, with each successive generation of cells becoming smaller.132
• Genetic Continuity: Each blastomere receives a full, identical complement of maternal and paternal chromosomes.32
• Structural Organization: As divisions continue, the blastomeres typically arrange themselves into a hollow, fluid-filled sphere known as a blastula. This structure features an outer layer called the blastoderm surrounding a central cavity, the blastocoel.24
• Variations: The pattern of cleavage is influenced by the amount and distribution of yolk within the egg. While some species undergo complete (holoblastic) division, others with significant yolk may exhibit partial (meroblastic) cleavage. In mammals, the process leads to the formation of a morula and subsequently a blastocyst.1234