When two parents homozygous for different alleles are crossed, the progeny (also called F1, for filial generation 1) is an heterozygote. F1 generations  of homozygous parents are very even; they are uniformly heterozygous. This is also true for commercial hybrid seed. In the following generation (F2) the alleles segregate independently, forming the basis for genetic variability. Sexual reproduction also introduces genetic variation due to recombination.