The Sources Of Genetic Diversity
It is completely random whether the maternal or paternal chromosome of each pair ends up at a particular pole. The orientation of each pair of homologous chromosomes on the metaphase plate is random, and a mixture of maternal and paternal chromosomes will be drawn toward the same cell pole by chance. This phenomenon is often called "independent assortment," and it creates new combinations of genes that are located on different chromosomes. Thus, we have two levels of gene reshuffling occurring in meiosis I. The first occurs during recombination in prophase I, which creates new combinations of genes on the same chromosome. In contrast to mitosis, the sister chromatids of a chromosome are not genetically identical because of the crossing-over process. Anaphase I then adds the independent assortment of chromosomes to create new combinations of genes on different chromosomes. A total of 223 (8.4 million) possible combinations of parental chromosomes can be produced by one person, and recombination further increases this to an almost unlimited number of genetically different gametes.