BIO380H5 Lecture Notes - Zona Pellucida, Confocal Microscopy, Cell Adhesion Molecule
Document Summary
Cleavage is the first event that occurs after fertilization. It converts the unicellular egg into a multicellular embryo. Cell differentiation and morphogenesis are not synonymous: growth: increases the size of a cell, tissue, organ or organism. Mitotic divisions maintain the diploid (2n) complement of the genome. The normal cell cycle has four phases; growth phase 1, (g1), dna. Synthesis (s), growth phase 2 (g2) and mitosis (m). There is no g1 and g2 phase during cleavage and hence cleavage cells become smaller in size. Since each blastomere has a diploid nucleus, the amount of nuclear dna in the embryo also doubles. The zygote is surrounded by the zona pellucida which is separated from the cell itself by the perivitelline space. The first cleavage/ division gives a two-celled embryo i. e. two blastomeres. Now the embryo has double the dna content of the zygote and it has made membrane to surround both cells.
