BLG 400 Lecture Notes - Lecture 7: Oogonium, Cell Division, Chromosome Segregation
Document Summary
Telophase ii: chromosomes begin to uncoil, nuclear envelopes and nucleoli re-form. Cytokinesis: cytoplasm divides forming 4 haploid cells. Meiosis contributes to genetic diversity in 2 ways: Independent assortment of non-homologues creates different combinations of alleles. Crossing over between homologues creates different combinations of alleles within each chromosome. Meiosis: occurs in germ cells as part of the sexual cycle, two rounds of division (meiosis i and ii, only diploid cells undergo meiosis, occurs after mitosis. None are identical to eachother or the original cell. Germ-line: specialized diploid cells set aside during embryogenesis. Oogonia: diploid germ cells in ovaries of female embryos. Divide by mitosis and enter meiosis i to become primary oocytes. Primary oocytes arrest in diplotene stage of meiosis i until after birth. At puberty, one oocyte per month resumes meiosis. At ovulation, completion of meiosis i produces a secondary oocyte and first polar body. Secondary oocyte arrests in metaphase of meiosis ii.