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Bio 305 Lecture 13:
Introduction to Quantitative Genetics
Feb 19, 2009
Dr. Long
Required reading:
Prelecture reading below and Chapter 18.
Be sure to read 669673.
Relevant end of chapter problems: Chapter 18 (1,2,58,14)
Course pack problems:
4454
Vocabulary:
additive effect
average effect
candidate genes
correlation
genetic correlation
phenotypic correlation
covariance
familiality
genetic markers
genetic variance
heritability
broad sense heritability
narrow sense heritability
mean
mid parent value
norm of reaction
quantitative trait loci
selection differential
selection response
truncation selection
standard deviation
variance
phenotypic variance
additive genetic variance
dominance variance
environmental variance
Learning goals:
Based on the reading and lecture material from this lecture, you need to be able to:
1.
Describe quantitative traits using the mean and the variance.
2.
Use the correlation coefficient to measure the similarity of relatives.
3.
Calculate the average effect and additive effect of genes.
4.
Use the norm of reaction to characterize phenotypes as a response to genes and
environments.
5.
Partition genetic variance into components related to additive and dominance effects.
6.
Determine which traits will respond best to selection, based on their heritability.
7.
Determine the placement of a QTL relative to molecular markers given phenotypic
and genotypic information from a backcross.
1
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View Full Document 13.1 Quantitative Traits
Many traits vary on continuous scales.
Some examples are stature, weight, blood pressure, and
blood glucose.
Geneticists call these traits quantitative to distinguish them from traits like blood
types whose values that fall into discrete categories.
Everyone is aware that family members
resemble each other for quantitative traits.
Genes influence quantitative trait expression and
inheritance.
Nongenetic factors in the environment also contribute to quantitative trait
expression.
Both the nature of gene action and the influence of environment prevent quantitative
traits from following Mendelian modes of inheritance.
Some important goals in quantitative genetics are:
•
to determine whether genes contribute to the variation in a quantitative trait.
•
how important is genetic variation as a source of phenotypic variation.
•
what is the strength of transmission from parents to offspring.
•
what are the phenotypes of the various genotypes in different environments.
•
what is the nature of genetic and genomic contributions to the quantitative trait?
How
many genes contribute? How are they distributed throughout the genome?
Do different
genes contribute equally, or are there some genes that play a major role?
13.2 Important Statistical Tools
Central tendency and dispersion:
The first step in genetic analysis of a quantitative trait is to
describe its distribution in the population.
The population distribution of a quantitative trait, say
Y, is usually described by its
mean
Y
μ
and
variance
2
Y
σ
.
For a sample of size N individuals, we
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This note was uploaded on 10/24/2009 for the course BIO 305 taught by Professor Wittkopp/csankovzski during the Winter '08 term at University of Michigan.
 Winter '08
 Wittkopp/Csankovzski
 Genetics

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