One gene comes from each parent for every trait. Each trait is passed from generation to generation. When gametes are formed, genes separate. If there are two unlike genes, one may be seen while the other is hidden. The inheritance of each trait is determined by units or factors that are passed on to descendants unchanged, and individual inherits one such unit from each parent for each trait, a trait may not show up in an individual but can still be passed on to the next generation and also the genes for each trait segragate themselves during gamete production.