This is because the Crossing over during meiosis cause is a homologous chromosomes to exchange alleles resulting in new combos of alleles in the offspring. Crossing over occurs between prophase 1 and metaphase 1 and is the process where homologous pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes. It can also happen during mitotic division, which may result in loss of heterozygosity.
