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GenPsychDevelopment1-1

GenPsychDevelopment1-1 - Heritability Slides and Narrative...

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Page 1 Heritability Slides and Narrative Text of narrative begins on page 5 below. Heritability Behavioral Genetics Behavioral genetics is concerned with the influence of genes on psychological function. All behavior depends on both heredity and environment. Gene expression is continually influenced by the environment. Examples from the textbook: Social support and shyness. Phenylketonuria The Heritability Quotient An estimate that quantifies the extent to which variations of a variable in a population can be accounted for by genetic differences among the individuals in the population. The quotient ranges from 0 (heredity accounts for none of the differences among individuals) to 1 (heredity accounts for all the differences) for a given characteristic. Variation Recall our discussion of descriptive statistics from earlier in the course. The standard deviation and the variance tell us how much variation exists among the values observed in a set of measurements. These two terms are mathematically equivalent, since the standard deviation is just the square root of the variance. The choice to use one or the other is based on which term makes it easier to perform a mathematical calculation or on which term makes it easier to think about an issue clearly. Heritability Estimates Variation, not Quantity Consider the following set of weight measurements, taken from genetically identical triplets: 145 lbs. 150 lbs. 120 lbs. Since the genes of all three individuals are identical, the heritability quotient has to be 0. Concluding that the variation in these measurements is due entirely to environmental factors (e.g., diet and exercise) is NOT to say that weight is uninfluenced by genetics. Without genes, weight would be 0 because the individual would not exist!
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Page 2 Visualizing the Heritability Quotient The heritability quotient represents the amount of variation attributable to genetics. Heritability quotient = .1 Heritability quotient = .3 Heritability quotient = .7 Heritability quotient = 1.0 Example: Heritability Quotient = 1 The variation among human beings in eye color is entirely due to genetic factors. Therefore, the heritability quotient for eye color is 1. Example: Low Heritability Quotient The variation in preference for baseball teams is entirely (or almost entirely) due to environmental and experiential factors, such as: Where a person was born. The color of the team uniform. The preferences of family members or friends. Etc. Therefore, we would expect the heritability quotient for baseball team preference to be close to 0.
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Page 3 A Tough Question What would you say the heritability quotient is for the number of eyes that people have?
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