Which mechanism increases genetic variation by random orientation of chromosome pairs during meiosis I?

• A. Crossing over
• B. Independent assortment
• C. Mutation
• D. Linkage

Answer: (B)

Genetic variation from random orientation of chromosome pairs during meiosis I comes from independent assortment. In metaphase I, each pair of homologous chromosomes lines up at the cell’s center, and which member of the pair (maternal or paternal) goes into a given gamete is determined independently for each pair. This means the gamete can end up with many different combinations of maternal and paternal chromosomes across all chromosome pairs. For humans, this creates 2^23 (tens of millions) possible chromosome set combinations in gametes, even before considering any recombination within chromosomes. Crossing over during prophase I also increases variation, but that involves exchanging segments on chromosomes rather than the random alignment of entire chromosome pairs. Mutation introduces new alleles, and linkage (genes close together on a chromosome) can reduce independent assortment, so it’s not the mechanism described by random orientation.