Genotypetophenotype

Genotype-to-phenotype describes the relationship by which the genetic constitution of an organism determines its observable traits. The genotype consists of the organism's heritable alleles at numerous loci, while the phenotype includes morphology, physiology, biochemistry, and behavior. The mapping from genotype to phenotype is mediated by gene expression, regulatory networks, developmental programs, and environmental influences, and it can be affected by epigenetic marks that modify gene activity without changing the DNA sequence.

Key concepts include penetrance and expressivity; incomplete penetrance means some individuals with the genotype do not display the trait; variable expressivity means trait severity varies. Traits can be monogenic or polygenic. Monogenic traits are determined largely by a single gene, though modifiers can exist; polygenic traits are influenced by many genes, often with small effects, interacting with environment.

Examples include diseases with strong genotype-phenotype associations such as sickle cell disease and cystic fibrosis, as well as polygenic traits like height, eye color, and skin pigmentation. Environmental factors such as nutrition and exposure can influence phenotypes. In many cases, genotype provides probability rather than certainty of a phenotype.

Applications and methods involve genetic association studies, quantitative trait locus mapping, transcriptomics, and model organisms to elucidate genotype-phenotype links. In medicine, genotype-to-phenotype information supports diagnosis, prognosis, and personalized treatment; in agriculture and breeding, it guides selection and improvement.

Limitations include incomplete knowledge of regulatory networks, pleiotropy, epistasis, and gene–environment interactions; differences among populations; and the measurement of complex traits.