What function does recombination by crossing-over have in genetic variation?

Answer: Crossing-over allows the genes that come from each parent to recombine before they are passed on to future generations because chromatids of homologous chromosomes mate and exchange sections of their DNA.

Explanation:

Chromosome crossing-over is the process by which chromatids of homologous chromosomes mate and exchange sections of their DNA during prophase I of meiosis, when pairs of homologous chromosomes, or of the same type, are aligned. The chromatids of the homologous chromosomes break off in the chiasmas and rejoin to allow recombination of the linked genes. So it occurs when regions at chromosome breaks mate and then reconnect to the other chromosome. The result of this process is an exchange of genes, called genetic recombination.

This allows the genes that come from each parent to recombine before they are passed on to future generations. Then, it is an important source of genetic variability, since it involves an exchange of segments between homologous chromosomes during the development of gametes. This process allows that the descendants of an individual are genetically very different, since it is very unlikely that an individual produces two equal gametes, because all of them have different segments of the homologous chromosomes.