BIOL 3445 Lecture Notes - Lecture 11: Heritability, Allele Frequency, Total Variation

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1 May 2018
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BIOL 3445.001 | Lecture #11 | 2/20/2018
Heritability
OBJECTIVES
Understand why some traits are normally distributed
Identify the sources of phenotypic variation
What does heritability (h2) mean?
Why is only narrow-sense heritability useful to predict a trait’s response to
selection?
QUATITATIVE GENETICS
Population Genetics: focuses on how evolution changes allele frequencies
o Bottom up approach
Quantitative Genetics: focuses on how evolution changes phenotypes
o Top down approach
Most phenotypic traits are quantitative
o Exhibit continuous variation
o Controlled by many loci/alleles
o Influenced during development by the environment
Quantitative traits tend to be normally distributed
o Population Mean*: the average trait value of the population
o Population Variance*: a measure of the spread of the variation around
the mean
PHENOTYPIC VARIATION
Where does all the variation we see in phenotypes come from?
o VTOTAL = VGENETIC - VENVIRONMENTAL
o The genetic portion of the total variation is heritable
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Document Summary

Understand why some traits are normally distributed. Population genetics: focuses on how evolution changes allele frequencies: bottom up approach. Quantitative genetics: focuses on how evolution changes phenotypes: top down approach. Most phenotypic traits are quantitative: exhibit continuous variation, controlled by many loci/alleles. Quantitative traits tend to be normally distributed: population mean*: the average trait value of the population, population variance*: a measure of the spread of the variation around the mean. Where does all the variation we see in phenotypes come from: vtotal = vgenetic - venvironmental, the genetic portion of the total variation is heritable. Narrow sense heritability (h2): the proportion of the total variation that is transmitted from parents to offspring: h2 = vgenetic/vtotal. H2 can vary between 0 and 1: the larger h2 is for a trait, the more closely the offspring will resemble their parents. If h2 = 0: the traits are strongly determined by the environment.

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