BIO380H5 Lecture Notes - Lecture 3: Zona Pellucida, Inner Cell Mass, Demethylation
Document Summary
Cleavage: the first event that occurs 24h after fertilization. It is a rapid mitotic cell division that converts unicellular egg into a multicellular embryo. Cleavage takes about 12-24 hours between each division. Only cleavage is happening, there is no growth. So the embryo size is ~ 0. 1mm in diameter. Cell number in the embryo increases exponentially. Blastomeres: the daughter cells that result from each cell division. It is a mitotic division, so the cell maintains its 2n diploid component (2n 2c before dna replication, 2n 4c after dna replication) Cleavage involves rapid cell division with no growth phases (g1 or g2) After fertilization, the ovum is similar to the somatic cell (one nucleus formed by two pronuclei). 1n 1c pronuclei are united, each chromo will search for the homologue, and then arrange themselves like a somatic cell. Immediately the cell has to produce more cells. Each cell division from fertilized ovum should have a duplication of the dna before division.
