Final answer:
Crossing-over occurs during prophase I of meiosis, where genetic material is exchanged between non-sister chromatids of homologous chromosomes. This process creates unique combinations of genes, contributing to genetic variation. In spermatogenesis, crossing-over and recombination occur, shuffling and exchanging genetic material between homologous chromosomes.
Step-by-step explanation:
Crossing-over occurs during prophase I of meiosis, where genetic material is exchanged between non-sister chromatids of homologous chromosomes. This exchange of genetic material creates unique combinations of genes, leading to genetic variation. It happens when homologous chromosomes line up in pairs and exchange segments of DNA, resulting in recombinant chromosomes.
During spermatogenesis, which is the process of sperm cell development, crossing-over and recombination occur. In the testes, diploid cells called spermatogonia undergo meiosis to produce haploid sperm cells. Crossing-over and recombination contribute to genetic variation in spermatogenesis by shuffling and exchanging genetic material between homologous chromosomes. This process creates new combinations of alleles and genes on each chromosome, leading to unique genetic traits in offspring.