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Genetics Chapter 17
Quantitative Genetics
| Term | Definition |
|---|---|
| quantitative genetics | genetic analysis of complex characteristics or characteristics influenced by multiple genetic factors |
| quantitative trait locus (QTL) | a gene or chromosomal region that contributes to the expression of quantitative characteristics |
| quantitative (continuous) characteristic | displays a large number of possible phenotypes, which must be described by a quantitative measurement |
| discontinuous characteristic | exhibits only a few, easily distinguished phenotypes. (seed shape) |
| as the number of loci encoding characteristic increases, the number of potential _________ increases. | phenotypes (differences between indiv. phenotypes become more difficult to distinguish |
| types of quantitative characteristics: meristic characteristics | characteristic whose phenotype varies in whole numbers, such as number of vertebrae |
| types of quantitative characteristics: threshold characteristics | discontinuous characteristic whose expression depends on an underlying susceptibility that varies continuously |
| polygenic characteristic | encoded by genes at many loci |
| ________ methods are required for analyxing quantitative characteristics | statistical |
| frequency distribution | a graph of the frequencies (numbers or proportions) of the different phenotypes |
| normal distribution | common type of frequency distribution that exhibits a symmetrical, bell-shaped curve |
| mean | statistic that describes the center of a distribution of measurements |
| variance | statistic that describes the variability of a group of measurements |
| _________ is used to estimate the proportion of variation in a trait that is genetic | heritability |
| heritability | the proportion of the total phenotypic variation that is due to genetic differences |
| phenotypic variance (Vp) | measures the degree of phenotypic differences among a group of individuals |
| what are three components of phenotypic variance? | genetic variance, environmental variance, and genetic-environmental interaction variance |
| components of phenotypic variance: genetic variance (Vg) | due to genetic difference among individual members of a population |
| components of phenotypic variance: environmental variance (Ve) | due to environmental differences among individual members of a population |
| components of phenotypic variance: genetic-environmental interaction variance (Vge) | results from an interaction between genotype and environment. genotypes are expressed differently in different environments |
| In summary, the total phenotypic variance can be calculated into three components: | Vp=Vg+Ve+Vge |
| what are three components of genotypic variance? | additive genetic variance, dominance genetic variance, genic interaction variance |
| components of genotypic variance: additive genetic variance (Va) | can be attributed to the additive effect of different genotypes |
| components of genotypic variance: dominance genetic variance (Vd) | can be attributed to dominance (interaction between genes at the same locus) |
| components of genotypic variance: genic interaction variance (Vi) | can be attributed to genic interaction (interaction between genes at different loci) |
| In summary, the total genetic variance can be calculated with the equation: | Vg=Va+Vd+Vi |
| We can now integrate these components into one equation to represent ALL the potential contributions to the phenotypic variance: | Vp=Va+Vd+Vi+Ve+Vge |
| Broad-sense heritability (H^2) | proportions of the phenotypic variance that is due to genetic variance |
| How is broad-sense heritability calculated? | by dividing the genetic variance by the phenotypic variance (Vg/Vp) |
| Narrow-sense heritability (h^2) | proportion of the phenotypic variance that can be attributed to additive genetic variance |
| How is narrow-sense heritability calculated? | by dividing the additive genetic variance by the phenotypic variance (Va/Vp) |
| Limits of heritability: it does not indicate the ______ to which a characteristic is genetically determined | degree |
| Limits of heritability: an ___________ does not have heritavility | individual |
| Limits of heritability: there is no _________ heritability for a charcertistic | universal |
| Limits of heritability: even when heritability is high, ___________ factors can influence a characteristic | environmental |
| Limits of heritability: heritability does not indicate the nature of __________ differences in a characteristic | population |
| Quantitative trait loci (QTL) | chromosome segments containing genes that control polygenic characteristics. |
| How can QTLs be mapped? | by examining the association between the inheritance of a quantitative characteristic and the inheritance of genetic markers |
| Genes influencing quantitative traits can also be located by using __________ __________ ______ | genomewide association studies |
| the amount that a quantitative characteristic changes in a single generation when subjected to selection is directly related to what? | to the selection differential and narrow-sense heritability |
| natural selection | arises through the differential reproduction of individuals with different genotypes |
| artiticial selection | promotion of the reproduction of organisms with traits perceived as desirable |
| selection differential | the difference between the mean phenotype of the selected parents and the mean phenotype of the original population |
| the response to selection (R) depends on narrow-sense heritability (h^2) and the selection differential (S) | R= h^2 x S |
| realized heritability | heritability determined by a response-to-selection experiment |
| When a characteristic has been selected for many generations, the response eventually _______ ___ | levels off (the characteristic no longer responds to selection) |
Created by:
cmccartney2
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