heritability Flashcards
Heritability
- the fraction of variation of any quantitative trait (phenotypic trait) that is caused by variation in genetics (i.e. genetic differences).
- Heritability is defined at the level of the population, not at the individual
- ranges between 0 and 1.0 on a scale
Heritability ROT
- high genetics, low environmental influence
- low genetics, high environmental influence
Heritability phenotypic variation ROT
If all the phenotypic variation in a group was due to genetic factors, heritability would have a value of 1
If all the phenotypic variation was due to environmental factors, heritability would have a value of 0
How to calculate heritability
- variance values given to complete these
- h^2 = VA / VT
- H^2 = VG / VT
- h^2 = (next gen-original) / (selected - original)
heritability: narrow sense calculation
- h^2 = VA / VT
- h^2 = (next gen - original) / (selected - original)
- most precise
- always measured by looking at parents and offspring
heritability: broad sense
- H^2 = VG / VT
- not as precise/accurate
Variance
- a measure of the spread numbers from the average (mean)
- three types are phenotypic variance, genetic variance, and environmental variance
Phenotypic variance
- total variance of the population, includes variation from genes and from the environment
- VP or VT
Genetic variance
- the variance that is due to variation among individuals in the alleles that they have, excludes environmentally-caused variation
- VG
Environmental variance
- environmentally-caused variation, excludes variation of alleles
- VE
Components of Genetic Variation
VG = VA + VD
VA: additive genetic variance, variation due to additive effects of alleles (polygenic traits with several unlinked allels, NOT epistasis)
VD: dominance genetic variation, variation due to dominance relationships among alleles (for single genomic locus, the dominant allele produces phenotypic effect no matter what the other allele is)
VP or VT = VG + VE
phenotypic variance = genetic variance + environmental variance
VG = VA + VD
Genetic variance = additive variance + dominance variance
VP or VT= VA + VD + VE
VPor VT= VG+VE
Phenotypic variance = additive variance + dominance variance (or together, genetic variance) + environmental variance
What happens to genetic equations when dealing with inbred population?
VT = VE because the VG = 0, the genetic variance equals zero
Explain missing narrow sense heritability
- Heritability that takes into account only those genetic factors that are additive
broad-sense heritability
- Heritability that takes into account all genetic factors
