To exhibit a recessive trait, an individual must have two recessive alleles responsible for the trait. One recessive allele is from a mother and another is from a father. However, if a person has one dominant and one recessive allele, it will not exhibit the recessive trait. This is because recessive allele will be masked by the dominant allele. So, parents must be heterozygous (one dominant and one recessive allele) and must give their recessive alleles to the offspring so that only offspring exhibit the recessive trait.
