Definition
Genotype refers to the genetic constitution of an organism, describing the specific alleles present at particular gene loci on its chromosomes. It encompasses all hereditary information encoded in DNA.
Explanation
The genotype of an individual determines the set of gene variants it carries and provides the blueprint for biological development. In diploid organisms, each locus contains two alleles that can be the same (homozygous) or different (heterozygous). The combination of alleles contributes to phenotypic traits, but environmental factors and gene interactions modulate the final outcome. Genotype can refer to a single gene (as in specifying the alleles of the hemoglobin β chain in sickle cell disease) or to the entire complement of genes, such as the genotype of a bacterial strain. Molecular techniques such as polymerase chain reaction, restriction fragment length polymorphism analysis and DNA sequencing are used to determine genotypes. Understanding genotypes is central to genetic mapping, breeding programs, disease diagnosis and studies of evolution because it reveals the genetic variation underlying traits. Distinguishing genotype from phenotype is important: two organisms with identical genotypes can display different phenotypes under different environmental conditions or epigenetic states.
Notable examples and facts
Examples of genotypes include the different combinations of ABO blood group alleles (IAIA, IAi, IBIB, IBi or ii) that determine blood type. Individuals with cystic fibrosis often have a homozygous ΔF508 deletion in the CFTR gene, whereas carriers have one normal and one mutant allele. In bacteria, antibiotic resistance genes such as a mutated rpoB conferring rifampicin resistance are part of the genotype. Genotype frequencies in populations are described by the Hardy–Weinberg principle, which predicts allele distributions under random mating. High-throughput genotyping arrays and whole-genome sequencing now allow rapid characterization of thousands of loci simultaneously.
Genotype captures the heritable code that guides an organism’s biology. By analysing genotypic variation, researchers and clinicians can predict traits, trace inheritance patterns and develop targeted therapies.
Related Terms: Phenotype, Allele, Homozygous, Heterozygous, DNA