What is needed for a recessive trait to be expressed?

A recessive trait is expressed in an individual when there are two copies of the recessive allele present. This is because recessive alleles do not manifest their traits unless paired with another recessive allele; they are overshadowed by dominant alleles. For instance, if an individual has one dominant allele (which expresses the dominant trait) and one recessive allele, the observable trait will reflect the dominant one due to its ability to mask the expression of the recessive allele. Only when both alleles are recessive can the specific trait associated with that recessive allele emerge, enabling the expression of the recessive trait.