During meiosis, which mechanism contributes to genetic variation?

• A. Crossing over between homologous chromosomes
• B. Mitosis of somatic cells
• C. Cloning of organisms
• D. Fusion of gametes

Answer: (A)

Crossing over between homologous chromosomes is how meiosis increases genetic diversity. During prophase I, paired homologs form a tetrad and non-sister chromatids exchange genetic material. This swap creates chromosomes with new combinations of alleles that aren’t present in either parent, so the gametes produced carry unique genetic makeups. The randomness of which chromatids participate and where the exchanges occur adds to the variation among offspring.

Mitosis of somatic cells produces identical daughter cells, so it doesn’t generate new allele combinations. Cloning is not a natural meiosis process. Fertilization (fusion of gametes) does combine genetic material to increase variation, but that occurs after meiosis, not as a mechanism within it.