Phenomenon in genetics that three or more alleles (example: A, a1) occur for a singular gene. A diploid plant contains just two alleles from this allelic series. As a result more than two phenotypes occur. Multiple alleles is a type of a non-Mendelian inheritance pattern.
For both multiple alleles and epistasis a 3:1 segregation ratio is very common in the offspring of a directed cross between two different phenotypes. An allelic test can give conclusive evidence which inheritance system applies.
RT: allelic test
BT: non-Mendelian inheritance