Quantitative and Behavior Genetics

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Quantitative and Behavior Genetics
Risk-seeking behavior
2

• Quantitative Genetics
• A. Types of Variation
• - discontinuous

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• Quantitative Genetics
• A. Types of Variation
• - discontinuous
• Qualitative - Categorical

frequency
white
purple
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• Quantitative Genetics
• A. Types of Variation
• - discontinuous
• Qualitative - Categorical

frequency
white
purple
order doesnt matter
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• Quantitative Genetics
• A. Types of Variation
• - discontinuous
• Qualitative - Categorical
• Quantitative - Meristic

frequency
10 15 20 25 30
order does matter ordinal scale.
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• Quantitative Genetics
• A. Types of Variation
• - discontinuous
• Qualitative - Categorical
• Quantitative Meristic
• - continuous
• Quantitative

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous - continuous

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical

No Contribution - Environmental
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Single Locus

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Multiple Loci Threshold Response
• many genes contribute to an increased
• probability of type II diabetes, in
• addition to environmental factors such
• as diet and exercise (multifactorial).

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Quantitative Meristic
• Multiple Loci polygenic
• Nilsson-Ehle (1909) wheat color

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Quantitative Meristic
• Multiple Loci polygenic
• Nilsson-Ehle (1909) wheat color

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Quantitative Meristic
• Multiple Loci polygenic

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• Qualitative - Categorical
• Quantitative Meristic
• Multiple Loci polygenic

¼ 1/41 One locus
1/16 1/42 two loci
Can model the number of genes contributing in an
additive way to a trait by determining genes (n)
necessary to explain the fraction of F2 offspring
that express a parental type (x). X
1/4n Measure x, estimate n. of categories
2n 1
1/64 1/43 three loci
1/256 1/44 Four loci
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• - continuous

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• - continuous

No Contribution - Environmental
Sun, water, soil nutrients
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• - discontinuous
• - continuous

Multiple Loci polygenic
Can model the number of genes contributing in an
additive way to a trait by determining genes (n)
necessary to explain the fraction of F2 offspring
that express a parental type (x). X
1/4n Measure x, estimate n. of categories
2n 1
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• - Broad sense heritability is the proportion
  of phenotypic variation in a population, in a
  given environment, that is due to genetic
  variation.

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• - Broad sense heritability is the proportion
  of phenotypic variation in a population, in a
  given environment, that is due to genetic
  variation.

So, suppose we observe variation in plant size
among genetically different plants growing in a
field This variation in phenotype might be due
to a combination of genetic and environmental
differences between them. V(phen) V(env)
V(gen)
H2 Vg/Vp
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• - Broad sense heritability is the proportion
  of phenotypic variation in a population, in a
  given environment, that is due to genetic
  variation.

IF these plants were all grown under the same
environmental conditions (common garden
experiment), then there is no variation in the
environment and the variation we observe can be
attributed to genetic differences. V(phen) 0
V(gen)
H2 Vg/Vp
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• - Broad sense heritability is the proportion
  of phenotypic variation in a population, in a
  given environment, that is due to genetic
  variation.

IF these plants were all grown under the same
environmental conditions (common garden
experiment), then there is no variation in the
environment and the variation we observe can be
attributed to genetic differences. V(phen)
V(gen) BUT this relationship is ONLY true in
this environment!!
H2 Vg/Vp
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

In a different environment, phenotypic and
genetic variation may be expressed
differently.
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

So, in a large population experiencing a range
of environments V(phen) V(env) V(gen)
V(ge)
V(ge) is a genotype by environment interaction
reflecting the fact that genotypes may respond in
different ways to changes in the environment.
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Suppose we had populations of each genotype, and
these were the mean heights of these populations.
Genotype C F
Height
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Suppose we had populations of each genotype, and
these were the mean heights of these populations.
Genotype C F
Height
XS
V(env)
XM
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Suppose we had populations of each genotype, and
these were the mean heights of these populations.
Genotype C F
Height
XC
V(gen)
XF
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Suppose we had populations of each genotype, and
these were the mean heights of these populations.
Genotype C F
Height

The effect of environment IS THE SAME for the two
genotypes (ge) 0.
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

So, in this comparison V(phen) V(env)
V(gen) V(ge)
Sig. Sig. ns
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Suppose we compare B and E.
Genotype B E
Height
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Environmental effects are significant
Genotype B E
Height
XS
V(env)
XM
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

Genetic effects are insignificant means dont
differ.
Genotype B E
Height
XC
XE
V(gen) 0
Stanford
Mather
Environment
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

There is a significant G x E interaction.
Genotype B E
Height
gtgt
The effect of environment IS NOT THE SAME for the
two genotypes!!
Stanford
Mather
Environment
34

• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability

In a different environment, phenotypic and
genetic variation may be expressed
differently. So, in this comparison V(phen)
V(env) V(gen) V(ge)
Sig. ns Sig.
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• - Broad sense heritability is the proportion
  of phenotypic variation in a population, in a
  given environment, that is due to genetic
  variation.
• - Narrow sense heritability is the proportion
  of phenotypic variation that is due to additive
  genetic effects as opposed to the effects of
  dominance or epistasis
• Vg Va Vd Ve h2 Va/Vp

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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• 2. Measuring Heritability
• a. Correlation See if the phenotype of the
  offspring correlates with the phenotype of the
  parents, in the same environment.

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Calculate the average phenotype of two parents,
and calculate the average phenotype of their
offspring. Graph these points across sets of
parents and their offspring. The slope of the
best-fit line (least-squares linear regression)
describes the strength of the heritability of
the trait.
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• 2. Measuring Heritability
• a. Correlation See if the phenotype of the
  offspring correlates with the phenotype of the
  parents, in the same environment.
• b. Experiment If most of the phenotypic
  variation is due to additive genetic variance,
  then the traits should respond quickly to
  selection.

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X1
Consider a population that varies for a given
trait, with mean X1
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X1
Consider a population that varies for a given
trait, with mean X1
Suppose some with an extreme phenotype are
selected for breeding, and they have mean Xb
Xb
The selection differential is computed as Xb
X1. So, if X1 5, and Xb 8, then the
selection differential 3.0
41
X1
Consider a population that varies for a given
trait, with mean X1
Suppose some with an extreme phenotype are
selected for breeding, and they have mean Xb
Xb
The selection differential is computed as Xb
X1. So, if X1 5, and Xp 8, then the
selection differential 3.0
Suppose the offspring from our breeding
population has the following distribution, with
mean X2
X1
X2
The response to selection X2 X1. If X2
6.5, then the response to selection 1.5.
42
X1
Consider a population that varies for a given
trait, with mean X1
Suppose some with an extreme phenotype are
selected for breeding, and they have mean Xb
Xb
The selection differential is computed as Xb
X1. So, if X1 5, and Xp 8, then the
selection differential 3.0
Suppose the offspring from our breeding
population has the following distribution, with
mean X2
X1
X2
The response to selection X2 X1. If X2
6.5, then the response to selection 1.5.
h2 r/s 1.5/3.0 0.5
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• Quantitative Genetics
• A. Types of Variation
• B. Genetic Contributions
• C. Estimating the Genetic Contribution to
  Phenotypic Variation
• 1. Heritability
• 2. Measuring Heritability
• a. Correlation See if the phenotype of the
  offspring correlates with the phenotype of the
  parents, in the same environment.
• b. Experiment If most of the phenotypic
  variation is due to additive genetic variance,
  then the traits should respond quickly to
  selection.
• c. MZ-DZ twin studies

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• Quantitative Genetics
• 2. Measuring Heritability
• c. MZ-DZ twin studies Vp Vg Ve
• - MZ twins Vg 0, so Vp for a trait only
  Ve.

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• Quantitative Genetics
• 2. Measuring Heritability
• c. MZ-DZ twin studies Vp Vg Ve
• - MZ twins Vg 0, so Vp for a trait only
  Ve.
• - DZ twins Us DZ twins to measure Vg Vp Ve
  (mz)
• - problem MZ twins are often treated more
  alike than DZ twins. So, many of their
  similarities may be environmental, too. Thus, Ve
  is underestimated.
• - when this artificially LOW Ve is subtracted
  from Vp for DZ twins, it OVERESTIMATES the
  genetic contribution to that trait.

For MZ twins, clothes choice shows very little
variation. (Ve 0.1).
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• Quantitative Genetics
• 2. Measuring Heritability
• c. MZ-DZ twin studies Vp Vg Ve
• - MZ twins Vg 0, so Vp for a trait only
  Ve.
• - DZ twins Us DZ twins to measure Vg Vp Ve
  (mz)
• - problem MZ twins are often treated more
  alike than DZ twins. So, many of their
  similarities may be environmental, too. Thus, Ve
  is underestimated.
• - when this artificially LOW Ve is subtracted
  from Vp for DZ twins, it OVERESTIMATES the
  genetic contribution to that trait.

For MZ twins, clothes choice shows very little
variation. (Ve 0.1). DZ twins dress different
(Vp 10.0). Vg Vp Ve 10.0 0.1 9.9 H2
for clothes wearing Vg/Vp 9.9/10.0 0.99.
WOW! WHAT A HUGE GENETIC CONTRIBUTION!!!
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• Quantitative Genetics
• 2. Measuring Heritability
• c. MZ-DZ twin studies Vp Vg Ve
• Hmmmm MZ twins are treated more similarly than
  DZ twins in their homes, so Ve differs between
  the groups. Hmmmm. Suppose we compare MZ and DZ
  twins reared apart, through adoption? Then Ve
  will be the same across groups, and greater
  similarity among MZ twins must be a function of
  greater genetic similarity.

MZ
DZ
Ve is the same for both groups
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• Quantitative Genetics
• 2. Measuring Heritability
• c. MZ-DZ twin studies Vp Vg Ve
• Greater similarity among MZ twins must be a
  function of greater genetic similarity.

Born in 1940. Reunited in 1979. both named Jim
by adoptive parents Both married women named
Linda. Then married women named Betty. Both had
sons named James Allen. Both had dogs named
Toy. Both liked Miller Lite. Both hated
baseball. Both raised in Ohio. Both had high
blood pressure. Both had vasectomies. Both had
migraines. Both were sheriffs. Both owned Chevys.
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• Quantitative Genetics
• Behavior Genetics
• Behaviors are complex responses to stimuli,
  dependent upon
• - genetically influenced capacity to receive
  stimuli
• - genetically influenced physiology integrating
  stimuli
• - genetically influenced physiological response
• - environmental context of the stimulus
• - environmental context of potential response

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• Quantitative Genetics
• Behavior Genetics
• Behaviors are complex responses to stimuli,
  dependent upon
• - genetically influenced capacity to receive
  stimuli
• - genetically influenced physiology integrating
  stimuli
• - genetically influenced physiological response
• - environmental context of the stimulus
• - environmental context of potential response

So, we should expect behaviors to be
multifactorial (environmental effects) with a
polygenic contribution.
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• Quantitative Genetics
• Behavior Genetics

Experimental Approach
Positive geotaxy
Negative geotaxy
52

• Quantitative Genetics
• Behavior Genetics

Experimental Approach
If you can select for a trait, it is heritable
and must have a genetic basis.
53

• Quantitative Genetics
• Behavior Genetics

Experimental Approach
Use genetic dissection to create genetically
different lines and examine their behaviors.
54

• Quantitative Genetics
• Behavior Genetics

Twin Approach
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• Quantitative Genetics
• Behavior Genetics

Comparative Microchip Approach