BIOL 2040 Lecture Notes - Lecture 10: Quantitative Genetics, Probability Distribution, Phenylketonuria
3 May 2018
School
Department
Course
Professor
Quantitative Genetics
October 29, 2015
• Quantitative traits in racehorses
• Quantitative traits in humans
o Swimming speed
o Intelligence
Continuous phenotypic variation: why?
1. Many genes (loci)
2. Environment: superimposition of truly continuous variation arising from nongenetic causes
Why we need quantitative genetics:
• Used to answer…
o What is the genetic and environmental contribution to phenotypic variation?
o How many genes influence the trait?
o Are the contributions of the genes equal?
o How do loci interact: additively? Epistatically?
o How do alleles at a locus interact: additively? With dominance?
o How rapid will the trait change under selection?
• Most traits are influenced by both environment and genetics
• >2 loci too complicated
Quantitative Traits:
• leaf indentation
• Cranium width
• Flower size
• Femur length
Kinds of Variation:
• Discrete or discontinuous
o Often determined by 1 gene
o Trait is either present or absent
o May be few classes of phenotype
• Continuous or quantitative
o Variations usually are determined by many genes and their environment
o Continuous phenotypic distance
•
Environment Matters:
• Physical traits depend on temperature
• Phenylketonuria – can be eliminated by avoiding phenylalanine in diet
Phenotypic Distribution:
• Adding environmental influences…
o On one genotype: deviations give rise to same distribution
o On all genotypes: entire distribution approximates a smooth normal curve
Quantitative Genetics (for a single individual)
P ~ G + E
• P= individual phenotype
• G= average phenotype with genotype in population
find more resources at oneclass.com
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Document Summary
October 29, 2015: quantitative traits in racehorses, quantitative traits in humans, swimming speed. Continuous phenotypic variation: why: many genes (loci, environment: superimposition of truly continuous variation arising from nongenetic causes. With dominance: how rapid will the trait change under selection, most traits are influenced by both environment and genetics, >2 loci too complicated. Quantitative traits: leaf indentation: cranium width, flower size, femur length. P ~ g + e: p= individual phenotype, g= average phenotype with genotype in population, e= environmental effect specific to individual. Quantitative genetics (for a population: mean of p ~ mean of g + mean of e, e=0, therefore, mean of p ~ mean of g. Variance: a measure of dispersion around the expected value, width of the frequency distribution (usually bell curve) Maze learning from 2 rat strains in 3 environments. Broad-sense heritability: hb changes if vg changes, hb changes if ve changes, hb is not a species-level characteristic.
