Two ways of generating genetic variation in meiosis

(a) Random assortment of maternal (blue) and paternal (purple) chromosomes at metaphase I. Here, three chromosome pairs (1, 2, and 3) have four possible orientations at metaphase I. In the haploid cells produced, there are eight possible combinations of maternal and paternal chromosomes. (b) Crossing over in prophase I increases genetic variation by generating new combinations of maternal and paternal alleles. The paternal chromosome (purple) carries the A and B alleles, while the maternal chromosome (blue) carries the a and b alleles. Crossing over between nonsister chromatids produces chromosomes carrying A and b, and chromosomes carrying a and B.