genotype

Genotype refers to the genetic constitution of an individual, or to the allelic composition at specific loci. It can denote the two alleles present at a gene (for example, AA, Aa, or aa) or the entire set of an organism's genes. The genotype provides the heritable information that can influence traits, and genotype frequencies are used in population genetics to describe how common particular variants are in a group.

An organism's phenotype—the observable characteristics—results from interactions between its genotype and the environment. Some traits are determined by a single gene and show Mendelian inheritance, with dominant and recessive alleles. Many traits are polygenic, shaped by multiple genes and their interactions, and may be heavily influenced by environmental conditions.

Common examples include human ABO blood types determined by the ABO gene, and cystic fibrosis caused by mutations in the CFTR gene when present in two recessive copies. In plant and animal breeding, selecting desirable genotypes helps improve traits such as yield, disease resistance, or tameness.

Genotypes are identified through DNA analysis, including sequencing, targeted genotyping assays, and SNP arrays. Population-genetics methods examine genotype frequencies and deviations from equilibrium, as in Hardy-Weinberg analyses, while genome-wide association studies link genotypes with traits.

Genotype information underpins medical diagnosis, personalized therapy, forensic analysis, and breeding programs. However, a given genotype does not guarantee a phenotype, especially for complex traits, and genetic information raises ethical and privacy considerations.