Transcript Chapter 15
Chapter 15 Complex Inheritance 15.1 quantitative traits 15.2 gene/environment interactions 15.3 artificial selection © 2006 Jones and Bartlett Publishers Up until now… traits have been discrete either round or wrinkled, either yellow or green, red eyes or white eyes,… a single gene has different alleles having different phenotypes very easy to study and understand But many traits are the result of interactions between multiple genes as well as being affected by the environment The traits are called: multifactorial traits quantitative traits multifactorial traits quantitative traits influenced by: alternative genotypes of one or more genes environmental factors inbred lines Fig. 15.1. A completely inbred line is homozygous for every gene © 2006 Jones and Bartlett Publishers multifactorial traits quantitative traits influenced by: alternative genotypes of one or more genes environmental factors example height continuous traits height, blood pressure, weight crop yield, milk production categorical traits ears of corn/stalk eggs from hen ridges in fingerprints threshold traits few phenotypes multiple genes/environement “predisposition to express” Quantification (how do we describe the results) “discrete” traits like seed color 75% yellow, 25% green continuous traits like height distributions mean, variance (std. deviation) mean = average sum of all heights divided by # of people measured 62” 65” 63” 70” 260 /4 = 65” = mean 54*5+ 56*33+ 58*254+… divided by 4995 =63.1 in. = mean height Table 15.1. Distribution of height among British women x fi xi N © 2006 Jones and Bartlett Publishers mean=average mean= sum of all heights divided by number of people Fig. 15.2. Graph of distribution of height among 4995 British women © 2006 Jones and Bartlett Publishers Fig. 15.3. A living histogram of human height © 2006 Jones and Bartlett Publishers mean variance? standard deviation? mean variance standard deviation fi xi x N f i x i x N 1 2 s2 = σ= s 2 mean = 63.1 inches variance = 7.24 inches2 std dev = 2.69 inches Fig. 15.2. Graph of distribution of height among 4995 British women © 2006 Jones and Bartlett Publishers 67% annotated bib. 95% 99.7% 36.3 = mean 2.4 = stdev bell curve Fig. 15.5. Features of a normal distribution © 2006 Jones and Bartlett Publishers Fig. 15.4. Variance of a distribution measures the spread of the distribution around the mean © 2006 Jones and Bartlett Publishers Variation in a trait genetic environmental •genotypic variation •environmental variation •variation due to genotypeby-environment interaction •variation due to genotypeby-environment association Variation in a trait genotypic variation due to differences in genotype the distribution of phenotypes, by itself, provides no information about how many genes influence a trait 3 genes affect trait A or a, B or b, C or c each dominant contributes some to phenotype Fig. 15.6. Segregation of independent genes affecting a quantitative trait © 2006 Jones and Bartlett Publishers 3 vs 30 genes? distribution is the same Fig. 15.7. Distribution of phenotypes determined by the segregation of 3 and 30 independent genes © 2006 Jones and Bartlett Publishers Variation in a trait genotypic variation due to differences in genotype the distribution of phenotypes, by itself, provides no information about how many genes influence a trait Variation in a trait environmental variation due to differences in environment inbred beans normal bell curve Fig. 15.8. Distribution of seed weight in a homozygous line of edible beans © 2006 Jones and Bartlett Publishers Fig. 15.8. Distribution of seed weight in a homozygous line of edible beans © 2006 Jones and Bartlett Publishers Variation in a trait environmental variation due to differences in environment the distribution provides no information about the relative importance of genotype or environment. Could be either/or or both Variation in a trait genetic and environmental variation when both affect phenotype independently, the total variance is the sum of the individual variances Fig. 15.9. Combined effects of genotypic and environmental variance © 2006 Jones and Bartlett Publishers Variation in a trait genetic and environmental variation when both affect phenotype independently, the total variance is the sum of the individual variances total = variance genotypic environmental + variance variance 2 p 2 g 2 e (eq. 15.3) Variation in a trait genetic and environmental variation REVIEW: •genotypic (G) variation •environmental (E) variation •variation due to G-E interaction •variation due to G-E association variation due to G-E interaction (genotype-by-environment) corn poor environment strain A does better than B good environment strain B does better than A e.g., special varieties of plants developed to suit different growing areas Fig. 15.10. Genotype-by-environment interaction in maize. [Data from W. A. Russell. 1974. Annual Corn & Sorghum Research Conference 29: 81] © 2006 Jones and Bartlett Publishers variation due to G-E (?) interaction (genotype-by-sex) sex different phenotype depending on gender of organism living histogram and height Fig. 15.3. A living histogram of human height © 2006 Jones and Bartlett Publishers variation due to G-E association (genotype-by-environment) cow example ? A homogeneous population… …will have no genotypic variance. 0 2 p Therefore: 2 g 2 g 2 e 2 p 2 e cave dwelling fish inbred inbred cross F1 homogeneous population cross F2 heterogeneous population see fig 15.6 Fig. 15.6. Segregation of independent genes affecting a quantitative trait © 2006 Jones and Bartlett Publishers inbred inbred cross F1 measure eye size variation homogeneous population cross F2 heterogeneous population inbred inbred cross F1 measure eye size variation 0.057 2 cross F2 0.563 2 F1 0.057 F2 0.563 2 e 0.563 0.057 2 e 2 2 2 e 2 p 2 g 0.506 2 g 2 g 2 e Which is more important genotype or environment? broad-sense heritability H2 shows the importance of genetic variation, relative to environmental variation, in causing variation in phenotype ratio of genotypic variance to total phenotypic variance 0.506 H 2 0.90 2 g e 0.563 2 2 g 2 p 2 g 90% of eye variation in fish is genetic Fig. 15.13. Selection for increased length of corolla tube in tobacco © 2006 Jones and Bartlett Publishers Fig. 15.13. Selection for increased length of corolla tube in tobacco © 2006 Jones and Bartlett Publishers M = mean of parental generation M* = mean of selected parents M’ = mean of progeny of selected parents M M h M ' 2 * M M M h * M M ' narrow-sense heritability 2 narrow-sense heritability M M h * M M ' 2 ratio of additive genetic variance to total phenotypic variance the broad-sense heritability H2 proportion of phenotypic variance due to genetic differences narrow-sense heritability h2 proportion of phenotypic variance due to differences in additive alleles that’s all from Chapter 15 for now folks © 2006 Jones and Bartlett Publishers