When is a recessive allele for a trait expressed in the phenotype of an dividual?

A recessive allele for a trait is expressed in the phenotype of an individual only when the individual is homozygous for that allele, meaning it has two copies of the recessive allele (one from each parent). If the individual has at least one dominant allele for that trait, the dominant trait will be expressed instead. Therefore, the presence of the recessive phenotype is only visible when both alleles are recessive.