Bio3400 1nd Edition Lecture 7 Outline of Last Lecture I Thomas Morgan II Gregor Mendel III The Modern Synthesis IV Hardy Weinberg Equilibrium V Peppered Moths Outline of Current Lecture I Heritability II Genes and Environment III Variation IV Broad sense heritability V Narrow sense heritability VI The Breeder s Equation VII The Selection Differential Current Lecture I Quantitative Genetics and Heritability a One challenge is quantifying how much phenotypic variation is due to variation in genetic factors and how much is due to variation in environment b Heritability the fraction of the total variation in a trait that is due to variation in genes c What would happen if we planted many clones genetically identical individuals in different fertilizers and selected on plant size II Genes versus Environment a Genes only operate within an environment these cannot be disentangled within an individual b Heritability is a population parameter c What percentage of the variation in the population is due to variation in genetic factors YES d What percentage of the height for an individual is because of their genes NO III Variation a Heritability the fraction of the total variation in a trait that is due to variation in genes b Variation Summation fruit size mean fruit size 2 number of fruits 1 These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute c Heritability Vg Vg Ve Vg Vp i Vg genetic variance ii Vp total variance phenotypic variance iii Ve environmental variance IV 2 types of heritability a Broad sense H 2 b Includes all genetic effects c H 2 Vg Vp d Narrow sense h 2 more important parents only pass an allele not a genotype e Includes only additive genetic effects f h 2 Va Vp g Alleles are passed on not genotypes therefore only additive effects are passed on V Measuring Heritability a Based on the observed and expected resemblance among relatives b Slope of the best fit line h 2 c Actual genetic similarity in a lab d Familiar similarity twins identical and fraternal VI The Breeder s Equation Predicting the response to selection a R Z h 2 S b Response to selection heritability selection differential VII The Selection Differential a What is S b S Mean breeders mean population c S 0 0 9 0 9 VIII R is the change in the mean trait value a New old IX Summary a The genetic component of quantitative traits can be estimated by looking at the phenotypic similarity of relatives b This estimate enables you to predict how a population will respond to selection c The magnitude of the response is directly proportional to the heritability for the trait in question d Quantitative genetics allows you to understand the genetic basis of virtually all aspects of the phenotype even if you do not know the specific genes involved
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