Genotype

Definition

The complete genetic constitution of an organism, or more commonly in practice, the specific set of alleles present at one or more genetic loci. In diploid organisms, which includes most insects and arachnids, each locus contains two alleles; when identical, the genotype is homozygous, when different, heterozygous. Genotype contrasts with phenotype, which is the observable expression of genetic and environmental interactions.

Etymology

From Greek genos (birth, race) + typos (mark, impression)

Example

In the mosquito Culex pipiens, the genotype at the Ester locus determines whether an individual carries resistance alleles (Ester^1, Ester^2) that confer organophosphate insecticide resistance; homozygous resistant genotypes survive higher chemical doses than heterozygous or susceptible genotypes.

Synonyms

• genetic constitution

Related Terms

• phenotype
• Allele
• homozygous
• heterozygous
• locus
• Genome
• haplotype
• Polymorphism

Usage Notes

Specialists distinguish between 'genotype' as the entire genetic makeup (rarely known in full) versus the allelic state at specific markers. In arthropod disease ecology, 'genotype' often refers to pathogen strains (e.g., West Nile virus genotype) rather than host genetics. The term is absolute for a given individual but relative when comparing populations or species.