allelerne

Allelerne are the different variants of a gene that occupy the same chromosomal locus in a genome. They arise through mutations and can differ in their DNA sequence or regulatory regions. In populations, allelerne contribute to genetic variation and can influence observable traits, disease risk, and response to treatment.

In diploid organisms, an individual carries two allelerne for most genes, one on each chromosome of a homologous pair. If the two are identical, the individual is homozygous for that locus; if different, heterozygous. Allelerne can have different modes of genetic interaction, including complete dominance, codominance, and recessiveness. For example, the ABO blood group system in humans involves several allelerne, IA, IB, and i; IA and IB are codominant, while i is recessive.

Populations may harbor many allelerne for a gene, a situation called polymorphism. Allele frequencies describe how common each allelerne is in a population. Under random mating, large populations approximately follow Hardy-Weinberg equilibrium, with genotype frequencies determined by the squared and product of allele frequencies (p^2, 2pq, q^2).

Evolutionary processes such as mutation, natural selection, genetic drift, migration, and recombination change allele frequencies over time. Allelerne underpin phenotypic diversity and are central to fields such as medical genetics, evolutionary biology, and forensic genetics.