Dominant Gene

A Dominant gene is an allele of an gene that gets expressed over a different allele when the organism has two different copies of a gene (and is therefore heterozygous). Black hair is dominant over blond hair in humans since when individual contains one copy of the gene for black hair and one for blond hair (therefore having a black and blond genotype), the black haired gene gets expressed and gives the individual a black-haired phenotype. However, this is a simplification of a complex process and many genes are not truly dominant.