Blond hair is a recessive trait. This means that a blond haired person is homozygous recessive or, in other words, pure breeding for blond hair because they have not received any dominant dark haired traits from either of their parents that they can pass on. So two blond parents will only have the alleles for blond hair in their genotypes. This means that all their offspring will usually ,by Mendelian rules, all be blond haired. But then there are always exceptions to the rules, such as mutations .
