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Lecture 12 - QG3 & Sexual selection

Lecture 12 - QG3 & Sexual selection - 1 Lecture...

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1 Lecture 12.1 - Quantitative Genetics, con't VI. Genotype x Environment Interaction (G x E) Not all genotypes have the same phenotype in every environment Figure, GxE e.g., the "Thrifty Gene(otype)": Alleles that confer susceptibility to diabetes and obesity in the modern environment were beneficial in the ancestral environment of uncertain resources. Thrifty genotypes can efficiently turn food into fat during periods of plentiful resources. So, Phenotypic value breaks down into: P = G + E + GxE, conclusions about V P follow VIII. Genetics and Evolution of Correlated Traits Phenotypic traits often do not appear to be independent. For example, human height and weight are positively correlated, as are human eye/hair/skin color. In many organisms, life-history traits are correlated, for example age-specific fecundity and age- specific growth often are negatively correlated. Traits can be correlated for strictly environmental reasons. To prove this to yourself, take a few cuttings from a plant that can be vegetatively propagated. Then water and fertilize one set and don't water or fertilize the other set. After a while, measure leaf size and leaf number. They will be positively correlated, even though the plants are genetically identical. In this case the phenotypic correlation is strictly environmental in nature. A. Causes of Genetic covariance 1. Pleiotropy (e.g., albinism, cave fish eyes/jaw/taste buds, Sry (sex-determining locus) figure of cave fish 2. Linkage disequilibrium - Hitchhiking - "Co-adapted gene complexes" (i.e., correlational /epistatic selection) - "Co-maladapted gene complexes" (individuals have different numbers of deleterious mutations * e.g., relaxation of constraint (classical cave-fish story) B. Statistics
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2 Recall covariance, Cov(X,Y) = ) )( ( y y x x p j i j ij i Covariance is a measure of association between variables. If large x tends to be found with large y and small x with small y, the covariance is positive. If large x tends to be found with small y and vice versa, the covariance is negative. Covariance can take on values of ± , and depends on the scale of the variable. Correlation r = Cov(X,Y) / ) ( ) ( Y Var X Var ; scales ± 1; 1 is a perfect positive association, -1 is a perfect negative association. C. Response to selection on correlated traits - If traits are phenotypically correlated, selection on trait X will result in selection on trait Y. If traits are genetically correlated, selection on trait X will produce a response in trait Y. -
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Lecture 12 - QG3 & Sexual selection - 1 Lecture...

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