Two pairs of twins give birth to different children. Twins can also be categorized as identical twins and heterozygous twins, and two pairs of identical twins give birth to different children, then heterozygous twins give birth to even more different children. Identical twins are two fetuses that develop from a single fertilized egg, such that the two children born have exactly the same genome; heterozygous twins are twins that develop from different fertilized eggs, such that the two children have different genomes. Therefore, children born from heterozygous twins with different genomes must be different. In the case of two pairs of identical twins with the same genome, their children are often different because the genes need to be rearranged and combined, so their children often have different sequences of gene combinations, and so their children are different.