Crossing over during meiosis increases genetic variation by exchanging segments between homologous chromosomes.

• A. True
• B. False
• C. It only occurs in mitosis
• D. It reduces chromosome number

Answer: (A)

Crossing over during meiosis increases genetic variation by exchanging segments between homologous chromosomes. In prophase I, homologous chromosomes pair up and form a tetrad; non-sister chromatids cross at points called chiasmata and swap DNA segments. This creates chromatids with new combinations of alleles, so the gametes—and ultimately offspring—have greater genetic diversity. This event happens only in meiosis, not mitosis, and it doesn’t by itself change the chromosome number—the reduction in chromosome number occurs due to the two meiotic divisions, not because of crossing over.