Exam 2: Set 3: QTLs and Heritability

quantitative trait (QT)

1. continuous distributions

2. affected by many genomic loci as well as environmental factors

3. categorized as anatomical, physiological, or behavioral

quantitative trait locus (QTL)

the region on a chromosome associated with a quantitative trait

multifactorial diseases

human diseases that are quantitative traits (i.e. autism, heart disease, etc).

phenotypic plasticity

when one genotype can have multiple different phenotypes as a result of environmental factors like diet, stressors, etc.

epistasis

the interaction of multiple genes effecting a single phenotypic trait

synergistic epistasis

genes work together to enhance the phenotype, whether in a beneficial or deleterious way

antagonistic epistasis

genes work against each other to lessen the impact of the phenotype, whether in a beneficial or deleterious way

pleiotropy

when one genomic locus works on multiple phenotypic traits (i.e. master regulators)

additive alleles

different from epistasis, where two mutated genes work together to increase/decrease the normal phenotype

total/phenotypic variance (V_P or V_T)

the total variance as a sum of genetic and environmental variance (V_G+V_E)

genetic variance (V_G)

the effect of different genotypes on phenotypic variation in a population, further divided into additive and dominance variance (V_A+V_D)

environmental variance (V_E)

the effect of environmental differences on phenotypic variance in a population

additive genetic variance (V_A)

variance in a trait due to the individual effects of alleles adding together without interactions from other alleles/genes

dominance genetic variance (V_D)

the additive/epistatic effect of alleles on a trait as a sum of the traits acting alone
Not directly inherited from parent to offspring but as a result of interaction of the parental alleles together or against each other

heritability

the phenotypic variance in a population due solely to genetic factors

broad-sense heritability (H²)

ratio of total genetic variance (V_G) and total phenotypic variance (V_T);
H²=V_G/V_T

narrow-sense heritability (h²)

the ratio of additive genetic variance (V_A) to total phenotypic variance (V_T), and the variability proportion that can be passed from parent to offspring;
h²=V_A/V_T

The closer h² is to 1, the greater the role genetic variance plays on phenotypic variance in a population

the downfall of heritability values

doesn’t account for the role of environment on total variance

who is heritability calculations most valuable for?

domestic and lifestock animal breeders who want to find the genetic contribution of specific traits (i.e. snake breeders and certain morphs, dog breeders and specific traits, etc)