multiallelic

Multiallelic refers to a genetic locus at which more than two alleles are present in a population. An individual can carry at most two alleles for a given locus, but the population may display several different alleles at that site. This contrasts with biallelic loci, where only two alleles are common in the population.

Common examples of multiallelic loci include short tandem repeat markers (STRs or microsatellites) and the ABO blood group system. In the ABO system, the I^A, I^B, and i alleles produce the observed A, B, AB, and O phenotypes, with expression governed by dominance and metabolic pathways. Highly polymorphic loci such as human leukocyte antigen (HLA) genes also exhibit many alleles and high diversity.

Multiallelic variation increases genetic diversity and has important implications for population genetics, forensic analysis, and linkage studies. More alleles per locus provide greater information content and discrimination power, but they also complicate statistical analyses, such as tests for Hardy-Weinberg equilibrium and calculations of genotype frequencies. Measures like observed and expected heterozygosity and polymorphic information content (PIC) are commonly used to summarize multiallelic marker diversity.

In practical applications, multiallelic markers are analyzed using allele frequency estimates, genotype inventories, and sometimes haplotype analyses. For forensic genetics, STRs are particularly valued for their high allelic diversity, which improves individual identification. In research, multiallelic loci facilitate fine-scale population structure analyses and disease association studies when appropriately modeled.