Which term describes an allele that is fully expressed in the phenotype, masking the recessive trait?

• A. Dominant Trait/Allele
• B. Recessive Trait/Allele
• C. Homozygous
• D. Heterozygous

Answer: (A)

Dominance in genetics explains why one allele can determine the trait even when a second, different allele is present. An allele that is fully expressed in the phenotype and masks the recessive trait is called the dominant allele. In any organism with at least one copy of the dominant allele, the dominant trait appears in the phenotype, whether the genotype is heterozygous or homozygous for the dominant allele. The recessive trait only shows up when both copies are recessive (homozygous recessive). The term recessive refers to that hidden trait, not to what is visible when a dominant is present. Homozygous describes having two identical alleles—which could be two dominant or two recessive—and doesn't by itself specify which trait is expressed. Heterozygous means having two different alleles (one dominant, one recessive), and in such cases the dominant trait typically masks the recessive one. Therefore, the term that describes the allele fully expressed and masking the recessive trait is the dominant allele.