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| Description: Meiosis is used to make sperm and egg cells. A shows a simplified version and B shows a detailed version. During meiosis, a cell’s chromosomes are copied once, but the cell divides twice. For simplicity, we have illustrated cells with only three pairs of chromosomes. The purpose of meiosis is to make haploid germ cells from diploid cells. In males, four haploid germ cells will be made by one meiotic division. In females, only one of the two cells created at the first cell division will go on to further cell divisions. The other is lost as a polar body. That cell will complete only the second cell division if fertilization occurs, and one of the two newly created cells will be expelled as a polar body. Figure A shows spermatogenesis and oogenesis, in which a cell is copied twice, but then only divides once each. Figure B shows a detailed view of this process. In the first meiotic division, there are 6 phases as follows. interphases, prophase 1, prometaphase 1, metaphase 1, anaphase 1, and telophase 1. In prophase 1, the matching chromosomes from your mother and father pair up. In prometaphase 1, while paired up, the maternal and paternal chromosomes can swap matching sections. This process, called crossing over, increases genetic diversity. In the second meiotic division, the last phase divides into 2, called cytokinesis, and these each undergo the following 6 phases. prophase 2, prometaphase 2, metaphase 2, anaphase 2, and telophase 2. These then go through cytokinesis again, resulting in 4 cells. The four daughter cells have half as many chromosomes as the parent cell and are called haploid. Picture Stats: Views: 65 Filesize: 477.31kB Height: 1900 Width: 2108 Source: https://biology-forums.com/index.php?action=gallery;sa=view;id=49613 |