Multiallele

Multiallele refers to a genetic locus that displays more than two alternative alleles within a population. In contrast to biallelic loci, multiallelic loci can harbor several distinct alleles at appreciable frequencies, increasing the level of polymorphism at that position. Multiallelicity is common in highly diverse or repetitive regions and is a defining feature of markers such as microsatellites and certain blood group or immune-related genes.

In population genetics, the diversity of a multiallelic locus is described by allele frequencies for each allele and by measures such as expected heterozygosity (H_e) and the effective number of alleles. H_e is calculated as 1 minus the sum of squared allele frequencies and reflects the genetic variability at the locus. Researchers often report the number of alleles per locus and allelic richness, which accounts for sample size. Rare alleles contribute to diversity but can complicate analyses due to low counts.

Examples of multiallelic loci include the ABO blood group system (A, B, and O alleles) and the highly polymorphic human leukocyte antigen (HLA) genes. Microsatellites, or short tandem repeats, are classic multiallelic markers used in forensic genetics, kinship analysis, and population studies because of their high allelic diversity.

Applications and analyses often treat multiallelic loci using allele-based tests, genotypic models, or haplotype approaches. When necessary, rare alleles may be collapsed into a common category to maintain statistical power. Multiallelic data provide rich information for studying genetic structure, diversity, and evolutionary processes, but they require careful statistical handling and interpretation.