1. Quantitative Genetics *discontinuous variation *continuous variation *Kolreuter – continuous phenotypic variation in tobacco plants *Multiple-factor hypothesis

2. Additive Alleles Intermediate More variation Variation, but similar to F 2

3. Quantitative Genetics

4. Polygenic Inheritance *Statistical Analysis Normal frequency distribution:Variance: *Mean *Variance *Standard Deviation *Standard Error

5. Polygenic Inheritance *Complex traits *multifactorial Glazier, A. et al. 2002. Finding Genes That Underlie Complex Traits. Science, 298, p.2345-2349

6. *Phenotype depends on environment and genes Nature vs. Nurture: The Genetics View

7. The expression of some genes is influenced by environmental factors, such as temperature Some alleles are heat-sensitive *Arctic foxes make fur pigment only when the weather is warm Nature vs. Nurture: The Genetics View

8. *Genetic control *Heritability H 2 = V G VPVP h 2 = V G V P + V E But,P = G + E TraitHeritability (% h 2 ) Mice Tail Length60 Body Weight37 Litter Size15 Chickens Body Weight50 Egg Production20 Egg Hatchability15 Cattle Birthweight51 Milk Yield44 Conception Rate3 Estimates of Heritability for Traits in Different Organisms

9. Nature vs. Nurture: The Genetics View TraitMZDZ Blood Types10066 Eye Color9928 Mental Retardation9737 Hair Color8922 Handedness7977 Epilepsy7215 Schizophrenia6910 Diabetes6518 Identical Allergy595 Cleft Lip425 Clubfoot323 Comparison of Concordance of Various Traits Between Monozygotic (MZ) and Dizygotic (DZ) Twins