week 5 prob session notes

week 5 prob session notes - Week 5 Quantitative &...

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Week 5: Quantitative & Population Genetics Page 1 of 10 Fall 2009 Week 5 – Quantitative & Population Genetics Qualitative vs. Quantitative ٠ Characters of kind ٠ Characters of degree ٠ Discontinuous variation ٠ Continuous variation (discrete phenotypic classes) (phenotypic measurements form a spectrum) ٠ Single-gene effects ٠ Polygenic control ٠ Individual matings and many ٠ Population of organisms with their progeny mating possibilities required to analyze ٠ Analysis involves counts and ratios ٠ Analysis involves statistical estimates of population parameters (i.e. mean, standard deviation, etc.) In order for a trait to be quantitative, it must be: - Quantitative Measurement - Measurement of an Individual - Shows Variability in the Population - Has Unknown Genetics/Environment - Ignores Ordinal and Qualitative Traits Quantitative traits are controlled by multiple genes, each segregating according to Mendel's laws. These traits can also be affected by the environment to varying degrees. Questions Studied in Quantitative Genetics 1. What is the genetic and environmental contribution to the phenotype? 2. How many genes influence the trait? 3. Are the contributions of the genes equal? 4. How do alleles at different loci interact: additively? epistatically? 5. How rapid will the trait change under selection? HERITABILITY Key Terms H 2 Broad Sense Heritability h 2 Narrow Sense Heritability V(P) Phenotypic Variation V(G) Genotypic Variation V(E) Environmental Variation V(A) Additive Genetic Variation V(D) Non-Additive Genetic Variation
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Week 5: Quantitative & Population Genetics Page 2 of 10 Fall 2009 What is it? The proportion of observed variation in a particular trait that can be attributed to inherited genetic factors in contrast to environmental ones. Put a little more simply: If we consider a trait such as IQ, Heritability tells us how much of the variation we see in IQ is because of genes versus the environment. There are a few concepts about Heritability that you need to be familiar with in order to effectively answer questions – See Section 7.4 of your Notebook. Equation for Broad Sense (yes, you need to memorize this formula): H 2 = V(G)/V(P) = V(G)/[V(G) + V(E)] So … If H 2 is high V(G) is large & V(E) is small Phenotypic selection will be effective Changes in environment will have little effect if any If H 2 is low V(G) is small & V(E) is large Phenotypic selection will not be effective Changes in environment may be effective Equation for Narrow Sense: h 2 = V(A)/[V(G) + V(E)] = V(A)/[V(A) + V(D) + V(E)] What is it NOT ? Does NOT measure the amount that genes are involved in a trait. Does NOT measure the relative importance of genes and environments for a trait. Is NOT an immutable part of the species.
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This note was uploaded on 12/10/2009 for the course GN 311 taught by Professor Emigh during the Spring '09 term at N.C. State.

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week 5 prob session notes - Week 5 Quantitative &...

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