Genes have different forms which are known as alleles.
In diploid organisms, like man and the higher animals, there are TWO alleles - one on each chromosome of the homologous pair. When those chromosomes undergo segregation during gametogenesis, one gamete would obtain the allele for white and the other the allele for black. - thus the resulting germ cells could pass on either the allele for black or the allele for white, but not both because of segregation of the homologous chromosomes. Capital letters are used to designate dominant genes. A recessive gene is the one over-ridden by the dominant gene. Recessive genes are designated by small letters.