Final answer:
Crossing over during meiosis I results in recombinant chromosomes with a unique combination of genes, contributing to genetic variation in the haploid daughter cells produced by meiosis.
Step-by-step explanation:
Crossing over is a critical process that occurs during prophase I of meiosis I, where there is an exchange of genetic material between homologous chromosomes. This exchange results in new combinations of genes, producing genetic variation. When homologous chromosomes pair up, non-sister chromatids can swap sections of DNA, thus forming recombinant chromosomes. These recombinant chromosomes lead to the production of haploid daughter cells with a unique set of genes, different from the parent cells. An example of the resulting genetic diversity can be seen in the possible recombinants: Ab, AB, ab, and aB when genes B and b cross over.These crossover events are the very first source of genetic variation produced by meiosis. They introduce a combination of maternal and paternal genes within a single chromosome that did not previously exist, contributing to the genetic uniqueness of gametes. Subsequent random assortment during metaphase I adds another layer of variation, as chromosomes segregate independently into gametes.