The behavior of chromosomes during meiosis and fertilization is responsible for most of the variation that arises each generation during sexual reproduction. Independent assortment of chromosomes contributes to genetic variability due to the random orientation of tetrads at the metaphase plate. or Because of recombination and independent assortment in meiosis, each gamete contains a different set of DNA. This produces a unique combination of genes in the resulting zygote. Recombination or crossing over occurs during prophase I .
