Which term describes the allele that masks others in a heterozygous combination?

• A. Penetrance
• B. Genotype
• C. Dominant allele
• D. Phenotype

Answer: (C)

In Mendelian genetics, the allele that determines the visible trait when two different alleles are present is the dominant allele. When an organism carries two different alleles (a heterozygous genotype), the dominant allele masks the effect of the recessive one in the phenotype. The recessive allele only appears when there are two copies (homozygous recessive). For example, if tall is dominant over short, a plant with the genotype Tt will be tall because the tall allele dominates the short allele. Penetrance refers to how consistently a genotype expresses a trait, genotype is the actual pair of alleles, and phenotype is the outward trait you observe. Therefore, the allele that masks the other in a heterozygous combination is the dominant allele.