Class Notes (836,147)
Canada (509,656)
Biology (1,909)
BIOL 4150 (48)
Lecture 14

lecture 14.doc

2 Pages
86 Views
Unlock Document

Department
Biology
Course
BIOL 4150
Professor
Scott Brandon
Semester
Winter

Description
Measuring Heritable Variation • Basic tenets of Darwin’s theory of evolution by natural selection: o If there is heritable variation among the individuals in a population, and if there are differences in survival and/or reproductive success among the variants, then the population will evolve. • Quantitative genetics includes tools to measure heritable variation, tools for measuring differences in survival and/or reproductive success, and tools for predicting the evolutionary response to selection • Quantitative genetics allows us to analyze evolution by natural selection in traits controlled by many loci • The first step in a quantitative genetic analysis is to determine the extent to which the trait in question is heritable. That is, we must partition the total phenotypic variation (V ) into a component due to genetic p variation (VG) and a component due to environmental variation (V ) E • Heritability- fraction of the total variation in a trait that is due to variation in genes o In the broad sense, that fraction of the total phenotypic variation in a population that is caused by genetic differences among individuals; in the narrow sense, that fraction of the total variation that is due to the additive effects of genes. • Phenotypic Variation (V )- tPtal variation in a trait • Genetic Variation (V )- Gariation among individuals that is due to variation in their genes • Environmental Variation (V )- vaEiation among individuals due to variation in their environments • Broad-Sense Heritability or Degree of Genetic Determination: Heritability = V / V = V / (V + V ) G P G G E Estimating Heritability from Parents and Offspring • If the variation among individuals is due to variation in their genes, then offspring will resemble their parents • Figure 9.13: o [9.13a] If offspring do not resemble their parents, then the slope of the best-fit line through the data will be near 0; this is evidence that the variation among individuals in the population is due to variation in their environments, not variation in their genes o [9.13c] If offspring strongly resemble their parents, the slope of the best-fit line will be near 1; this is evidence that variation among individuals in the population is due to variation in their genes, not variation in their environments o [9.13b] Most traits in most populations fall somewhere in the middle, with offspring showing a moderate resemblance to their parents; this is evidence that the variation among individuals is partly due to variation in their environments and partly due to variation in their genes • Narrow-sense Heritability (h )- that fraction of the total phenotypic variation in a population that is due to the additive effects of genes o Is an estimate of the fraction of the variation among the parents that is due to variation in their genes h = V AV P V /A(V +AV + D ) E 2 • Heritability, h , is a measure of the (additive) genetic variation in a trait • Additive genetic variation (V ) isAvariation among individuals due to the additive effects of genes • Dominance genetic variation (V ) is vDriation among individuals due to gene interactions such as dominance o total genetic variation is the sum of the additive and dominance genetic variation  V G V +AV D • Narrow sense heritability, h , allows us to predict how a population will respond to selection Estimating Heritability from Twins • Monozygotic (identical) twins share their environment and all of their genes • Dizygotic (fraternal) twins share their environment and half of their genes • If heritability is high, and variation among individuals is due mostly to variation in genes, then monozygotic twins will be more similar to each other than are dizygotic twins • If heritability is low, and variation among individuals is due mostly to variation in environments, then monozygotic twins will be as different from each other as dizygotic twins Measuring Differences in Survival and Reproductive Success • Second tenet of Darwin’s theory: o There are differences in survival and/or r
More Less

Related notes for BIOL 4150

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit