What term describes more than two alleles for a genetic trait?

• A. Polygenic traits
• B. Incomplete dominance
• C. Multiple alleles
• D. Test cross

Answer: (C)

In genetics, a gene can have more than two alternative forms in a population. These different forms are called multiple alleles. An individual, however, can carry at most two of these alleles—one on each chromosome—while the population as a whole can harbor many variants. A classic example is the ABO blood type gene, which has three common alleles (often labeled IA, IB, and i). The combinations of these alleles in individuals produce the different blood types, illustrating how more than two alleles can exist for a single trait.

Other concepts describe different ideas. Polygenic traits involve a trait influenced by many genes, not the number of alleles for one gene. Incomplete dominance refers to a heterozygote phenotype that is intermediate between the two homozygotes. A test cross is a method used to determine an unknown genotype by crossing with a homozygous recessive.