воскресенье, 10 октября 2010 г.
Schematic representation of maturation division (meiosis).
In order to provide a better overview, the course of the two maturation divisions is exemplified in a germ cell with three pairs of chromosomes (red chromosomes = paternal, blue chromosomes = maternal). During the pachytene of the prophase of the first maturation division, the chromatids become visible. The maternal and paternal chromosomes arrange themselves next to each other and form a tetrad (two chromosomes each with two chromatids). During this process the paternal and maternal chromatids partly overlap and when they separate there is an interchange of fragments (“crossing-over”). During themetaphase of the first maturation division, the homologous (paternal and maternal) chromosomes separate, and are randomly distributed to the two daughter cells. This process creates two haploid daughter cells each with a single set of chromosomes. During the second maturation division, the two daughter chromatids separate by mitotic cell division, so that the first and second maturation divisions result in the creation of four haploid sex cells. (After Beske)