OnRamps Biology Practice Test

Genetic variation in meiosis mainly comes from two events that shuffle alleles in different ways: crossing over and independent assortment. During prophase I, homologous chromosomes pair up and nonsister chromatids exchange segments, creating chromosomes with new combinations of alleles—the recombinants. Then, during metaphase I, the way chromosome pairs line up and separate is random, so the mix of maternal and paternal chromosomes in each gamete varies; this is independent assortment. Together, these two processes produce a wide array of possible allele combinations in gametes.

Crossing over alone would miss the variation generated by which parental chromosome each gamete ends up with, and independent assortment alone would miss the new allele combinations created by recombination. A mutation during mitosis isn’t a regulated meiotic mechanism for generating the diversity seen in offspring, and it occurs in somatic cells rather than within the meiotic processes themselves. So the most complete explanation is that both crossing over and independent assortment contribute to genetic variation during meiosis.