Which allele type masks the effect of its paired allele?

• A. Dominant allele
• B. Recessive allele
• C. Gene
• D. Trait

Answer: (A)

In Mendelian genetics, the dominant allele is the one that masks the effect of the other allele in a heterozygous individual. When an organism has one copy of a dominant allele and one copy of a recessive allele, the trait associated with the dominant allele appears in the phenotype. The recessive trait only shows up when both alleles are recessive. For example, tall (dominant) masks short (recessive) in a Tt plant, so the plant is tall; only tt would be short. The other terms—gene and trait—describe a unit of heredity and a visible characteristic, respectively, but they don’t explain how one allele hides the expression of its paired allele.