Which mechanism is primarily responsible for introducing genetic variation in offspring?

The correct choice involves crossing over, which is a crucial mechanism during meiosis, the process that generates gametes (sperm and eggs) in sexually reproducing organisms. During prophase I of meiosis, homologous chromosomes pair up and exchange segments of genetic material in a process called crossing over or recombination. This exchange results in new combinations of alleles on each chromosome, thereby introducing genetic variation in the gametes produced. When these gametes fuse during fertilization, the resulting offspring inherit a unique mix of genetic traits from both parents, increasing genetic diversity within a population.

This variation is essential for evolution and adaptation in changing environments, as it provides a pool of potential traits that natural selection can act upon.