Answer and Explanation:
Variation refers to the differences among living organisms. Some of the variations are shown in tongue rolling, fingerprints, height and weight. Variations can be categorised into two types; discontinuous and continuous variations. Variation in the physical appearance of organisms is caused either by genetic, environmental factors or a combination of both.
During gamete formation, crossing over would occur. during prophase 1 of meiosis, homologous chromosomes pair to form bivalents. The chromatids of bivalents form intimate contact points called chiasmata. At the chiasma, breakage may occur and exchange of chromatids segments between non-sister chromatids may take place. This is called crossing-over.