Genetic Mix Dizygotic twins Olivia and Harrison have half their genes in common, as do all siblings from the same parents. If the parents are close relatives, who themselves share most alleles, the non-shared half is likely to include many similar genes. That is not the case here, as mother (Nicola) is from Wales and father (Gleb) is from the nation of Georgia, which includes many people of Asian ancestry. Their phenotypes, and the family photos on the wall, show many additive genetic influences.