Under which condition are autosomal recessive traits expressed?

Autosomal recessive traits are expressed when an individual has two recessive alleles for a particular gene. In this genetic model, both alleles must be recessive in order for the trait to be phenotypically visible. This means that an individual with one recessive allele paired with a dominant allele will not express the recessive trait, as the dominant allele masks the effect of the recessive one. Therefore, the expression of an autosomal recessive trait specifically requires that both alleles responsible for that trait be the recessive form, which is why having two recessive alleles present is the correct condition for expression.