Answer:
One dominant allele
Step-by-step explanation:
Two alleles are needed in any one locus, and they can either be dominant or recessive. Since a dominant allele will hide the expression of the recessive allele, only one dominant allele is needed in the parents. In other words, one parent must contribute a dominant allele and the other parent can contribute either a dominant or a recessive allele. The resulting phenotype will have the dominant phenotype in all cases.