BIOB 375 1st Edition Lecture 34 Outline of Last Lecture I. Biotechnology Outline of Current Lecture II. Quantitative geneticsIII. Qualitative traitsCurrent LectureQuantitative Genetics1. What are quantitative traits?2. How to distinguish quantitative traits?3. What are the common features of quantitative traits?4. How to study quantitative traits?Qualitative traits- Discontinuous characteristicso Human blood types A, B, AB, and O typeso Phenotypeo Extreme height groupsQuantitative traits:- Continuous characteristics o Plant height- Meristic characteristic (countable trait)o # of puppies for a female dogo # of tillers/planto # of seeds/head- Threshold characteristic o Resistant vs. Susceptible Monogenic inheritance- Difference between two individuals, one locusPolygenic inheritance- More than one gene, more than one locusQuantitative traits are influenced by environmental factorsCommon features of qualitative and quantitative traits:Qualitative traits- A few distinct phenotypes- Monogenic- Less influenced by environmental factorsQuantitative traits- Continuous phenotypes- Polygenic- Influences by environmental factorsHow to study quantitative traits?Population and phenotyping- Replicate populationso Individuals in the population are homozygous at all loci- Phenotype is the mean of the same genotypes in different environmentsThe mean, the variance and the standard deviation- For example: seed sets of a planto At least three heads were counted form each planto 25 seeds, 35 seeds, 31 seeds The mean X = (25+35+31)/3 = 30.33 The variance s^2 = [(25-30.33)^2+(35-30.33)^2+(31-30.33)^2]/(3-1) = 25.34 The standard deviation s = √25.34 The greater the variance, the more spread out the distribution is about the meanPhenotypic variance- Genetic variance- Genetic-environmental interaction variance- Environmental variance How to estimate the proportion of each factor?Statistics methods for analyzing quantitative characteristics- Correlation and regressiono Correlation describes the relation between two or more variableso Regression defines the relation between two variables- Molecular markers for quantitative trait loci (QTL)
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