An allele is a different form of a gene that is located in a specific place on a chromosome that controls a specific trait and is responsible for genetic variation. Alleles are inherited from parents, two per gene, one from each parent. Therefore, an allele is one of a pair of alleles. Hair color is decided by alleles (sequence variations) of the gene that controls hair color. One allele might possess the trait for blond hair and another allele that of black hair. The resulting hair color depends on the alleles interaction. When an organism has two different alleles (i.e., blond trait, black trait), it is called heterozygous. When the alleles are the same, it is called homozygous.