Alleles are different forms of a gene present in a population. Most of the time there are two forms of allele in which one is dominant and another is recessive. These alleles can be present in homozygous and heterozygous form.
In homozygous both the alleles are of the same type that means both are dominant or both are recessive but in heterozygous both the allele are of different type that means one dominant and one recessive.
So the dominant allele can express itself in heterozygous condition but the recessive allele can only express itself in the homozygous condition. So recessive allele should be present on both the chromosomes to be expressed. Therefore the correct answer is recessive allele.
