4: Quantitative genetics Flashcards
What are the 3 types of phenotypic variation?
Discontinuous (categorical/mendelian)
Continuous (quantitative/complex/multifactoral)
Threshold variation
Describe discontinuous variation
- No intermediates
- Follows mendelian ratios
- Simple genetic basis, limited environ effect
E.g height, blood groups, red/white pea flowers
Describe continuous variation
- Phenotypes don’t fall into classes
- Offspring of intermediate phenotype
- Cannot observe mendelian ratios
- Complex genetic basis + environ
- Normal curve
E.g IQ, Dermal ridges (fingerprints), crop yield, weight gain in animals)
Describe threshold variation
- Appears like a discontinuous trait but is caused by a continuous distribution
- Distribution is called liability
- Phenotype depends on critical threshold
- No simple segregation in families
Define phenotypic variance
total variation within a pop. for a phenotype is measured by the phenotypic variance (Vp)
What are the 2 components of phenotypic variance?
Variation due to diffs in genotype → genetic variance VG
Variation due to environ effects → environmental variance VE
Define broad sense heritability
the proportion of the phenotypic variation in a pop. that is due to genetic differences among individuals
→ often expressed as a %
Why is heritability an excellent predictor for short-term but NOT long-term response?
(think about the influence of selection)
Allele frequencies change over time due to selection and/or genetic drift
- This change affects genetic variance (VG) and in turn heritability
- Also the effects of environ change over time so environmental variance (VE) can change too
The more heritable a trait is, the more likely it will respond to ________
selection
define norm of reaction
A way to view GxE as the response to environ variation as the quantitative trait
