Quantitative genetics, is the study of continuous traits (such as height, or weight)that do not have straight forward Mendelian inheritance because they result from the interaction of many different genes.

The field was founded, in evolutionary terms, by the originators of the modern synthesis, Ronald Fisher, Sewall Wright and J. B. S. Haldane, and aimed to predict the response to selection given data on the phenotype and relationships of individuals.

More recently quantitative genetics has come to include the analysis of quantitative trait loci. Traits that are under the influence of a large number of genes are known as quantitative traits, and their mapping to a location on the chromosome requires accurate phenotypic, pedigree and marker data from a large number of related individuals.

Quantitative genetic analysis is used to determine how heritable a trait is, and how will it respond to natural or artificial selection. This analysis also gives insight into how populations evolve.

Modes of inheritance

• Mendelian inheritance includes several different kinds of inheritance:
  • Discrete or simple inheritance, is where traits are controlled by a single locus with two alleles
  • Multiple alleles where a phenotype is determined by multiple interacting alleles.
• Non-Mendelian inheritance: in non-Mendelian inheritance, traits are not necessarily controlled or inherited according to the Mendelian laws.

Traits

• Continuous traits are quantitative traits have a continuous phenotypic range. They are usually polygenic, and may also have a significant environmental influence.
• Meristic traits are traits which are expressed in whole numbers, such as number of offspring, or number of bristles on a fruit fly.
• Discrete (threshold) traits are either expressed or not. Multiple genes may influence a discrete trait.

See also

• population genetics, built on some of the same principles as quantitative genetics
• Ewens's sampling formula