Which gene expresses a trait even if only one copy is present?

• A. Recessive Gene
• B. Dominant Gene
• C. Sex-linked Gene
• D. Polygenic Gene

Answer: (B)

A dominant allele is the one that expresses its trait even when only one copy is present. In a pair, if one chromosome carries the dominant variant and the other carries a recessive one, the dominant allele’s effect shows in the organism’s phenotype. Only when both copies are the recessive variant does the recessive trait appear. The other options don’t fit this pattern: a recessive trait needs two copies to be expressed, a sex-linked gene’s behavior depends on its chromosome location rather than just copy number, and a polygenic trait is influenced by many genes rather than a single dominant allele showing up with one copy.