Genetics of Complex Traits: Heritability, QTLs, and Mapping Techniques

Complex trait

A phenotype that is influenced by multiple genes and environmental factors, often showing continuous variation in a population.

Gene x environment interaction

A phenomenon where the effect of a genotype on a phenotype depends on the environment in which the organism develops.

Genotypic value

The average phenotype of individuals with a specific genotype, representing the contribution of the genotype to the trait value.

Phenotypic variance

The total variation observed in a trait within a population, resulting from both genetic and environmental differences.

Broad sense heritability

The proportion of total phenotypic variance that is attributable to all genetic variance, including additive, dominance, and epistatic effects.

Narrow sense heritability

The proportion of total phenotypic variance that is attributable specifically to additive genetic variance, which determines the resemblance between parents and offspring.

Epistasis

An interaction between two or more different genes where the effect of one gene is dependent on the presence of one or more 'modifier' genes.

Parent-offspring regression

A statistical method used to estimate narrow sense heritability by comparing the phenotypic values of parents to those of their offspring.

Average effect

The mean deviation from the population average of individuals that received a particular allele from one parent, averaged over all possible alleles received from the other parent.

Breeding value

The part of an individual's genotypic value that is due to additive gene effects and can be passed on to the next generation.

Breeder's equation

A formula (R = h^2 * S) used to predict the response to selection, where R is the response, h^2 is narrow sense heritability, and S is the selection differential.

Selection differential

The difference between the mean phenotype of the selected parents and the mean phenotype of the entire original population.

Response to selection

The change in the mean phenotype of a population in the next generation resulting from selection applied to the current generation.

Linkage mapping

A method used to identify the location of genes or quantitative trait loci on a chromosome based on the frequency of recombination between genetic markers.

Association mapping

A method for mapping quantitative trait loci that relies on linkage disequilibrium between markers and causal variants in a natural population.

Pedigree

A diagram or record of the ancestry of an individual, used to track the inheritance of traits or genes through generations.

Linkage likelihood

The probability of observing the data given a specific recombination frequency between two loci.

Likelihood ratio

A statistical test comparing the likelihood of the data under a hypothesis of linkage versus the likelihood under a hypothesis of no linkage.

LOD score

The log10 of the likelihood ratio, used to determine the strength of evidence for genetic linkage between two loci.

Quantitative trait locus (QTL)

A specific region of the genome that is statistically associated with the variation of a quantitative, complex trait.