If one allele is not phenotypically expressed in the presence of another, we say that it is a(an) allele

Recessive allele.

Explanation:

Mendel was known as the father of genetics. Mendel explained the concept of dominance, laws of segregation and the law of independent assortment by the experiments on pea plant.

The Mendel explained that the  pairs of the contrasting traits, one trait has the ability to express itself and hides the expression of other trait is known as dominant trait. The trait that is not able to express itself in heterozygous condition and express itself in homozygous recessive condition only known as recessive trait.

Thus, the answer is recessive allele.

this transfer is call conjunction

bru what tyep of qus is dis