Transcript ppt - eweb.furman.edu

Quantitative and Behavior Genetics
Risk-seeking behavior
I.
Quantitative Genetics
A. Types of Variation
- discontinuous
Quantitative Genetics
A. Types of Variation
- discontinuous
Qualitative - Categorical
frequency
I.
white
purple
Quantitative Genetics
A. Types of Variation
- discontinuous
Qualitative - Categorical
frequency
I.
purple
white
‘order’ doesn’t matter
Quantitative Genetics
A. Types of Variation
- discontinuous
Qualitative - Categorical
Quantitative - Meristic
frequency
I.
10
15
20
25
30
‘order’ does matter – ‘ordinal’ scale.
I.
Quantitative Genetics
A. Types of Variation
- discontinuous
Qualitative - Categorical
Quantitative – Meristic
- continuous
Quantitative
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
- continuous
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
female
male
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
No Contribution - Environmental
female
male
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
Single Locus
I.
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).
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
Quantitative – Meristic
Multiple Loci – ‘polygenic’
Nilsson-Ehle (1909) – wheat color
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
Quantitative – Meristic
Multiple Loci – ‘polygenic’
Nilsson-Ehle (1909) – wheat color
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
Qualitative - Categorical
Quantitative – Meristic
Multiple Loci – ‘polygenic’
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
¼ = 1/41
One locus
- discontinuous
Qualitative - Categorical
Quantitative – Meristic
1/16 = 1/42
two loci
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
1/64 = 1/43
three loci
1/256 = 1/44
Four loci
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
- continuous
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
- discontinuous
- continuous
No Contribution - Environmental
Sun, water, soil nutrients
I.
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
I.
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.
I.
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
I.
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
I.
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)
H2 = Vg/Vp
BUT this relationship is ONLY true
in this environment!!
I.
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.
I.
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(g*e)
V(g*e) is a genotype by environment
interaction; reflecting the fact that
genotypes may respond in different ways
to changes in the environment.
I.
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.
Height
Genotype
C
F
Stanford
Mather
Environment
I.
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.
Height
Genotype
C
F
XS
XM
Stanford
Mather
Environment
V(env)
I.
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.
Height
Genotype
C
F
XC
V(gen)
XF
Stanford
Mather
Environment
I.
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.
Height
Genotype
C
F
XCS
XCM = XFS
XFM
The effect of
environment IS
THE SAME for the
two genotypes:
(g*e) = 0.
Stanford
Mather
Environment
I.
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(g*e)
Sig.
Sig.
ns
I.
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.
Height
Genotype
B
E
Stanford
Mather
Environment
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
C. Estimating the Genetic Contribution to Phenotypic Variation
1. Heritability
Environmental effects are significant
Height
Genotype
B
E
XS
V(env)
XM
Stanford
Mather
Environment
I.
Quantitative Genetics
A. Types of Variation
B. Genetic Contributions
C. Estimating the Genetic Contribution to Phenotypic Variation
1. Heritability
Genetic effects are insignificant; means don’t differ.
Height
Genotype
B
E
XC
XE
V(gen) = 0
Stanford
Mather
Environment
I.
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.
Height
Genotype
B
E
XCS
XCM >> XFS
XFM
The effect of
environment IS
NOT THE SAME
for the two
genotypes!!
Stanford
Mather
Environment
I.
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(g*e)
Sig.
ns
Sig.
I.
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
I.
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.
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.
I.
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.
X1
Consider a
population
that varies
for a given
trait, with
mean = X1
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
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
Suppose the
offspring from
our breeding
population has
the following
distribution, with
mean = X2
The selection differential is
computed as Xb – X1. So, if
X1 = 5, and Xp = 8, then the
selection differential = 3.0
X1 X2
The response to selection =
X2 – X1. If X2 = 6.5, then the
response to selection = 1.5.
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
Suppose the
offspring from
our breeding
population has
the following
distribution, with
mean = X2
The selection differential is
computed as Xb – X1. So, if
X1 = 5, and Xp = 8, then the
selection differential = 3.0
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
I.
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:
I.
Quantitative Genetics
2. Measuring Heritability
c. MZ-DZ twin studies: Vp = Vg + Ve
- MZ twins: Vg = 0, so Vp for a trait = only Ve.
I.
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).
I.
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!!!
I.
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
“The Jim Twins”
Ve is the same for
both groups
I.
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.
“The Jim Twins”
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 Chevy’s.
I.
Quantitative Genetics
II. 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
I.
Quantitative Genetics
II. 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.
I.
Quantitative Genetics
II. Behavior Genetics
Positive geotaxy
Negative geotaxy
Experimental Approach:
I.
Quantitative Genetics
II. Behavior Genetics
Experimental Approach:
If you can select for a trait, it is
heritable and must have a
genetic basis.
I.
Quantitative Genetics
II. Behavior Genetics
Experimental Approach:
Use genetic dissection to create
genetically different lines and
examine their behaviors.
I.
Quantitative Genetics
II. Behavior Genetics
Twin Approach:
I.
Quantitative Genetics
II. Behavior Genetics
Comparative Microchip Approach: