Multiple alleles refer to a condition where a gene exists in more than two allelic forms. Typically, there are only two alleles for a gene in a diploid organism, but multiple allelism can occur when there are three or more allelic forms of a gene. These genetic variations arise usually through mutation and are responsible for hereditary variations. Although individual humans (and all diploid organisms) can only have two alleles for any given gene, multiple allele traits may exist at the population level, promoting variation within the same species. Some key characteristics of multiple alleles include:
- Multiple alleles of a gene occupy the same locus on the chromosome.
- Multiple alleles are the alternative forms of the same gene, so they influence the same trait.
- The wild-type allele is mostly dominant over the mutant alleles.
- A series of mutant alleles can exist in a population, generated by a spontaneous mutation in the wild type and the mutant alleles.
- Multiple alleles lead to the formation of varied phenotypic traits for a character in the population.
Examples of multiple alleles include the ABO blood groups, where there are multiple sequences that correspond to each of the three alleles Iᴬ, Iᴮ, and i. Another example is coat color in rabbits, where four alleles exist for the c gene.
