What is the term for an allele that does not manifest in the presence of a dominant allele?

The term for an allele that does not manifest in the presence of a dominant allele is known as a recessive allele. Recessive alleles require two copies to express their phenotype, meaning an individual must inherit one recessive allele from each parent for the trait to be observed. In contrast, dominant alleles can express their trait even when only one copy is present. Therefore, in a heterozygous situation where both a dominant and a recessive allele are present, only the dominant trait will be displayed, effectively masking the effect of the recessive allele.

Understanding this concept is crucial in genetics as the interaction between dominant and recessive alleles is a foundational principle of Mendelian inheritance, illustrating how traits are passed down through generations.