polymorphisms

Polymorphism in biology refers to the presence of two or more distinct forms within a population, species, or genome, maintained at appreciable frequencies. These forms can be phenotypes, genotypes, or both. A locus is considered polymorphic when at least two alleles occur at appreciable frequencies; otherwise it is often termed monomorphic.

Genetic polymorphisms are sequence variants that underlie variation among individuals. Common forms include single nucleotide polymorphisms (SNPs), insertions and deletions (indels), copy number variants (CNVs), and variable number tandem repeats (VNTRs). Some polymorphisms alter gene function or regulation and influence traits, disease risk, or drug response. Phenotypic polymorphisms, such as color morphs in animals or lactase persistence in humans, illustrate how genetic variation yields observable differences.

Population genetics studies examine allele frequencies and their changes under drift, migration, mutation, and natural selection. Neutral variants may drift; balancing or directional selection can maintain or shift frequencies. Detection methods include sequencing and genotyping arrays, with Hardy-Weinberg expectations providing a baseline for genotype frequencies.

Medical relevance: many diseases and drug responses correlate with polymorphisms in enzymes, transporters, or receptors; pharmacogenomics uses such data to guide therapy. Evolutionarily, polymorphisms contribute to adaptive potential and reflect historical pressures such as infection or diet.

Other uses: outside biology, polymorphism denotes multiple forms of a structure or data type, such as polymorphic functions or types in mathematics and computer science.