Final answer:
The condition whereby a trait is determined by three or more alleles is called multiple alleles. An example of multiple alleles is the ABO blood type system in humans, where there are three different alleles: IA, IB, and i.
Step-by-step explanation:
Multiple alleles refer to the existence of more than two different forms of a gene in a population. However, each individual typically possesses only two alleles, one from each parent. Multiple alleles contribute to genetic diversity, as they can result in various combinations and expressions of traits within a population, influencing phenotypic variation.
Thus, the condition whereby a trait is determined by three or more alleles is called multiple alleles. Multiple alleles occur when there are more than two different versions of a gene that exist in a population. An example of multiple alleles is the ABO blood type system in humans, where there are three different alleles: IA, IB, and i.