Q.Describe the process of cleavage that leads to blastocyst formation.

[!TLDR]

Repeated mitotic cleavage divisions carry the zygote through 2-, 4- and 8-cell stages to a solid morula, which then develops a fluid-filled blastocoel and reorganises into a blastocyst. …

Cleavage begins immediately after fertilisation, as the zygote divides mitotically while being carried along the fallopian tube toward the uterus. Successive divisions produce 2-, 4- and 8-celled stages; unusually, the daughter cells (blastomeres) become progressively smaller with each division, so overall embryo size stays roughly constant even as cell number rises, and the whole structure remains enclosed within the zona pellucida throughout. By around the time it reaches the uterine cavity, cleavage has produced a solid ball of about 8-16 cells, the morula. The morula continues dividing and its cells reorganise: a fluid-filled cavity, the blastocoel, ap …

Give the stages in strict sequence (zygote, 2-cell, 4-cell, 8-cell, morula, blastocyst) and note the two features that define a blastocyst …

Describing cleavage as increasing the overall size of the embryo -- cleavage divisions increase cell number without an intervening growth phase, so the embryo's overall size sta …