Genetic and Phenotypic Variation II Flashcards
Define quantitative genetic variation.
Variation among individuals in a phenotypic trait that is due to genetic differences at multiple Mendelian inherited loci.
How does quantitative genetic variation cause said variation to appear continuous?
The influence of multiple genes on a trait causes the variation to appear as continuous.
What is another term for quantitative genetic variation?
Polygenetic traits
Define each variable in this equation.
V means variance
Here we calculate total variance by summing:
Variance due to genotype, variance due to environment and variance due to error
What is genetic variance (Vg)?
The absolute variance in a trait due to genetic differences among individuals.
What is heritability?
The proportion of the total phenotypic variation in the population due to genetic differences among individuals.
What is the quantitative range for heritability values?
Heritability varies between 0 (no heritability) to 1 (complete heritability).
How is heritability calculated?
Vg/VTotal
What are the two main methods used to quantify heritability?
Parent-offspring regression
Family or sib-design
How does parent-offspring regression work?
- Estimates heritability by comparing trait similarity between parents and offspring
Outline the procedure for parent-offspring regression.
- Plot mean offspring value against mid-parental value
- Calculate the line of best fit using ordinary least-squares (OLS) regression (linear regression)
- The slope of this line = heritability
What are the two main benefits of parent-offspring regression?
o Allows you to directly study traits inherited between generations
o Allows estimation of heritability within natural populations
What are the two main limitations of parent-offspring regression?
o Assumes parents’ environment is the same as offsprings’ environment
o Changes in environment between generations can alter phenotypes
How does sib-design work?
- Estimates heritability by comparing traits among clones or siblings
Outline the procedure for sib-design.
- Grow/rear replicate offspring individuals from multiple clones or families
- Randomize a common environment
- Estimate variance among families/genotypes, environmental variance and error variance
- Calculate heritability = Vgenotype/Vtotal
What are the benefits of sib-design experiments?
o Common gardens allow heritability to be estimated without confounding effects of environment
o Flexible breeding designs
What are the two limitations of sib-designs?
o Not all species are willing to be reared in a common garden
o Obtaining adequate replication can be problematic
This was the general equation for determining total variance. However, Vgenotype can actually be broken into 4 subtypes of variance. What are they?
VAdditive
VDominance
VEpistasis
VMaternal/epigenetic
What is dominant genetic variance?
Variance due to dominant effects of alleles
What is epistatic genetic variance?
Variance due to interactions between alleles at different loci
What is maternal variance?
maternally inherited genetic (i.e., mitochondria, plastids) and environmental (provisioning) differences leading to variance.
What is epigenetic variance?
phenotypic variation due to epigenetic modifications
What is additive genetic variance?
most accurately predicts the response to selection
What are estimates of heritability based on additive genetic variance called?
Narrow-sense heritability
What are estimates of heritability based on genetic variance called?
Broad-sense heritability
What is this equation for? Define all variables.
Broad-sense heritability (H^2) equation
VG = genetic variance
VT = total variance
What is this equation for? Define all variables.
Narrow-sense heritability (h^2)
Va = additive genetic variance
VT = total variance
