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The Relationship Between Genotype and Phenotype

24.1 Quantitative Characteristics Vary Continuously and Many Are Influenced by Alleles at Multiple Loci. The Relationship Between Genotype and Phenotype For continuous characteristics: several different genotypes produce same phenotype. Types of Quantitative Characteristics.

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The Relationship Between Genotype and Phenotype

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  1. 24.1 Quantitative Characteristics Vary Continuously and Many Are Influenced by Alleles at Multiple Loci • The Relationship Between Genotype and Phenotype • For continuous characteristics: several different genotypes produce same phenotype.

  2. Types of Quantitative Characteristics • Meristic characteristics • Determined by multiple genetic and environmental factors, and can be measured in whole numbers. • Animal litter size. • Threshold characteristics • Measured by presence or absence • Susceptibility to disease

  3. Types of Quantitative Characteristics • Polygenic inheritance • Refers to quantitative characteristics controlled by cumulative effects of many genes. • Each character still follows Mendel’s rules. • Kernel color in wheat.

  4. Determining Gene Number For a Polygenic Characteristic • (1/4)n = number of individuals in the F2 progeny. • N = gene number.

  5. 24.2 Statistical Methods Are Required for Analyzing Quantitative Characteristics • Distribution • Frequency distribution • Normal distribution: a symmetrical (bell-shaped) curve. • Samples and populations • Population: group of interested individuals • Sample: small collection of individuals from the ppulation.

  6. 24.2 Statistical Methods Are Required for Analyzing Quantitative Characteristics • The mean: the average • The Variation and Standard Deviation • Variance: the variability of a group of measurements • Standard deviation: the square root of the variance.

  7. Correlation • Correlation: when two characteristics are correlated, a change in one characteristic is likely to be associated with a change in the other.

  8. Correlation • Correlation coefficient: measures the strength of their association • Correlation doesn’t imply a cause-and-effect relation. It simply means that a change in a variable is associated with a proportional change in the other variable.

  9. Regression • Regression: Predicting the value of one variable, if the value of the other is given. • Regression coefficient: represents the slope of the regression line, indicating how much one value changes on average per increase in the value of another varible.

  10. Concept Check 3 In Lubbock, Texas, rainfall and temperature exhibit a significant correlation of -0.7. Which conclusion is correct? • There is usually more rainfall when the temperature is high. • There is usually more rainfall when the temperature is low. • Rainfall is equally likely when the temperature is high or low.

  11. Concept Check 3 In Lubbock, Texas, rainfall and temperature exhibit a significant correlation of -0.7. Which conclusion is correct? • There is usually more rainfall when the temperature is high. • There is usually more rainfall when the temperature is low. • Rainfall is equally likely when the temperature is high or low.

  12. 24.3 Heritability Is Used to Estimate the Proportion of Variation in a Trait That Is Genetic • Heritability: The proportion of the total phenotypic variation that is due to genetic difference.

  13. Heritability • Phenotypic variation : Vp • Genetic variance: Vg • Va: additive genetic variance • Vi: genic interaction variance • Vd: dominance gentic variance

  14. Heritability • Phenotypic variation : Vp • Genetic variance: Vg • Environmental variance: Ve • Genetic-Environmental Interaction Vge • Vp = Vg + Ve + Vge • Vp = Va + Vd + Vi + Ve + Vge

  15. Heritability • Broad-Sense Heritability • H2 = Vg/Vp • If H2 = 0, then none of the phenotypic variance is caused by genetic variance. • If H2 = 1, then the phenotypic variance is 100% caused by genetic variance.

  16. Locating Genes That Affect Quantitative Characteristics • Mapping QTLs

  17. 24.4 Genetically Variable Traits Change in Response to Selection • Response to selection: the extent to which a characteristic subjected to selection changes in one generation. • Artificial selection: Selection by promoting the reproduction of organisms with traits perceived as desirable.

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