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Unformatted text preview: Bio 305 Lecture 13: Introduction to Quantitative Genetics Feb 19, 2009 Dr. Long Required reading: Pre-lecture reading below and Chapter 18. Be sure to read 669-673. Relevant end of chapter problems: Chapter 18 (1,2,5-8,14) Course pack problems: 44-54 Vocabulary: additive effect average effect candidate genes correlation genetic correlation phenotypic correlation covariance familiality genetic markers genetic variance heritability broad sense heritability narrow sense heritability mean mid parent value norm of reaction quantitative trait loci selection differential selection response truncation selection standard deviation variance phenotypic variance additive genetic variance dominance variance environmental variance Learning goals: Based on the reading and lecture material from this lecture, you need to be able to: 1. Describe quantitative traits using the mean and the variance. 2. Use the correlation coefficient to measure the similarity of relatives. 3. Calculate the average effect and additive effect of genes. 4. Use the norm of reaction to characterize phenotypes as a response to genes and environments. 5. Partition genetic variance into components related to additive and dominance effects. 6. Determine which traits will respond best to selection, based on their heritability. 7. Determine the placement of a QTL relative to molecular markers given phenotypic and genotypic information from a backcross. 1 13.1 Quantitative Traits Many traits vary on continuous scales. Some examples are stature, weight, blood pressure, and blood glucose. Geneticists call these traits quantitative to distinguish them from traits like blood types whose values that fall into discrete categories. Everyone is aware that family members resemble each other for quantitative traits. Genes influence quantitative trait expression and inheritance. Non-genetic factors in the environment also contribute to quantitative trait expression. Both the nature of gene action and the influence of environment prevent quantitative traits from following Mendelian modes of inheritance. Some important goals in quantitative genetics are: to determine whether genes contribute to the variation in a quantitative trait. how important is genetic variation as a source of phenotypic variation. what is the strength of transmission from parents to offspring. what are the phenotypes of the various genotypes in different environments. what is the nature of genetic and genomic contributions to the quantitative trait? How many genes contribute? How are they distributed throughout the genome? Do different genes contribute equally, or are there some genes that play a major role? 13.2 Important Statistical Tools Central tendency and dispersion: The first step in genetic analysis of a quantitative trait is to describe its distribution in the population. The population distribution of a quantitative trait, say Y, is usually described by its mean Y and variance 2 Y ....
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- Winter '08