Traits that are controlled by more than two alleles (for example ABO blood typing) are called

• A. Multiple allele traits
• B. Polygenic traits
• C. Monogenic with two alleles
• D. Allelic series

Answer: (A)

When a trait is governed by more than two alleles at a single gene locus, it’s called a multiple allele trait. In ABO blood typing, the gene responsible has three common alleles: IA, IB, and i. An individual carries two alleles, but the population has more than two possible alleles, which creates four possible blood types (A, B, AB, and O) depending on which two alleles are present and how they interact (IA and IB are codominant, i is recessive to both). This distinguishes it from polygenic traits (many genes contribute to one phenotype), monogenic traits with two alleles (one gene, two options), and an allelic series (a specific ordering of dominance among several alleles).