Final answer:
Crossover, or recombination, is a process during meiosis where homologous chromosomes exchange genetic material, leading to two recombinant and two parental gametes, contributing to genetic diversity.
Step-by-step explanation:
Crossover, or recombination, occurs between two pairs of homologs; this exchange produces two recombinant or crossover gametes and two parental gametes. During prophase I of meiosis I, homologous chromosomes align closely together and may exchange genetic material between their non-sister chromatids, leading to the creation of unique combinations of genes. Each pair of homologous chromosomes forms a configuration known as a tetrad, where crossover can happen at several points, resulting in recombinant chromosomes that carry a mix of maternal and paternal genetic information. Conversely, the chromosomes that do not undergo crossover maintain their original genetic composition and are known as non-recombinant or parental chromosomes. This process of recombination contributes significantly to genetic variation among gametes.