In genetic terms, what does a recessive allele require to express its trait?

A recessive allele requires the presence of another recessive allele to express its trait because recessive alleles only manifest their characteristics when an individual is homozygous for that trait. This means that both alleles at a particular gene locus must be the same and recessive in order for their traits to be expressed in the phenotype. In contrast, if there is a dominant allele present, it will eclipse the expression of the recessive allele, leading to the dominant trait being displayed instead. Thus, the identificable trait associated with the recessive allele only occurs when two copies of that allele are present, reinforcing the concept of recessive inheritance.