The alternative forms of that are present for a given gene are known as alleles.
Two types of alleles exist for any given gene - these are dominant allele and recessive allele.
A dominant allele is the one which always expresses itself in the presence of another allele, that is it can express itself in both heterozygous and homozygous situation.
A recessive allele is only able to express itself in a homozygous condition.
<em>Since the blond hair is not expressing itself in either the mother or father but only in the daughter, it must be a recessive allele.</em>
