Final answer:
Crossing over is a meiosis mechanism where homologous chromosomes exchange DNA, leading to genetic variation in gametes. It occurs during prophase I of meiosis I and, combined with independent assortment and random fertilization, contributes to an enormous potential for genetic diversity.
Step-by-step explanation:
Crossing over is a crucial mechanism in meiosis that contributes to genetic diversity in gametes. It happens during prophase I of meiosis I, when homologous chromosomes pair up and exchange segments of their DNA. This exchange is between non-sister chromatids and can occur at multiple locations, leading to the creation of new combinations of alleles on each chromosome. Genetic variation is therefore significantly increased due to crossing over.
Additionally, crossing over contributes to genetic diversity along with independent assortment and random fertilization. Independent assortment refers to the random orientation of chromosome pairs during meiosis I, which results in the production of gametes with different combinations of maternal and paternal chromosomes. Random fertilization further increases genetic variation because any sperm can fertilize any egg, leading to numerous possible combinations of parental chromosomes.