Greg has several siblings that all look very different from one another. however, he can see different traits from his mother and father in each of them. what contributed to these differences between his siblings? both prophase 1 and prophase 2 occurred during the formation of his parents' sex cells. independent assortment occurred during the formation of his parents' sex cells. independent assortment occurred during fertilization of each egg cell. in mitosis during growth, crossing over caused each child to develop differently.