Final answer:
Cells in eukaryotes generate DNA double-strand breaks (DSBs) during meiosis I, leading to meiotic homologous recombination. This exchange of genetic material between non-sister chromatids results in recombinant chromosomes and genetic diversity in gametes.
Step-by-step explanation:
Meiotic Homologous Recombination in Eukaryotes
During meiosis in eukaryotes, meiotic homologous recombination is a critical process for generating genetic diversity. This process commences early in prophase I, when homologous chromosomes align tightly in a pairing known as synapsis. Following this, recombination nodules facilitate the formation of DNA double-strand breaks (DSBs) at specific locations, initiating crossover events. The broken DNA ends are then processed and exchanged between non-sister chromatids, leading to a reciprocal exchange of genetic material. After the exchange, the DNA is ligated, connecting the homologous chromosomes at chiasmata. The result is the creation of new combinations of alleles on recombinant chromosomes, contributing to genetic variation among gametes.
Importantly, the machinery used for this recombination is the same as that used in DNA repair, ensuring that the process is highly accurate and prevents deleterious mutations. The stages of meiosis, including synapsis and chiasmata formation, ensure at least one crossover per chromosome--essential for the proper segregation of homologous chromosomes during the first meiotic division.