An allele that produces its phenotype only when paired with an identical allele is called what?

• A. Allele
• B. Genotype
• C. Recessive allele
• D. Dominant allele

Answer: (C)

The concept here is recessiveness in how alleles are expressed. A recessive allele only shows its trait when two copies are present, so it must be paired with an identical allele (homozygous recessive) for the phenotype to appear. If there’s a dominant allele present (even one copy), it will mask the recessive trait, which is why recessive traits only show up in the absence of a dominant allele. An allele is just a variant form of a gene, while a genotype refers to the actual pair of alleles an individual has, and a dominant allele is one that can express its trait with just one copy.