Discontinuous or Discrete

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Discontinuous or Discrete Qualitative
Continuous or Quantitative can be metric or
meristic
metric measured meristic counted (whole s)
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Determining the role of the environment on trait
expression
Keep genotypes constant and vary the environment
Example body length in some species is affected
by two genes (A and B) and the amount of protein
consumed in its first meal
Choose many AABB individuals and expose them to
different protein content first meals and then
measure body length attained. Then do the same
for all genotypes.
Choose one environment and expose individuals of
all genotypes to the selected protein content
first meals and then measure body length
attained. Then do the same for all reasonable
environments.
Regression Analysis R2 is a statistic of
relationship between variables
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All variation in phenotypes is due to the
experimental contribution (genes or environment),
r2 1
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No variation in phenotypes is due to the
experimental contribution (genes or environment),
r2 0
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Some variation in phenotypes is due to the
experimental contribution (genes or environment),
0 lt r2 lt 1
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Heritability How much of phenotypic variance
results from genetic variance
VP VG VE (we are the sum of our genes and
environment)
Broad Sense proportion of phenotypic variance
due to genetic variance H2 VG/VP
But not all genetic variance is created
equal Some is additive, some involves
interactions within or among loci. Additive
variance (VA) determines how much offspring
resemble parents. (Codominant alleles are
primarily additive expression does not depend
on other allele.) The effects of non-additive
(VNA) alleles on your phenotype depend on what
other alleles you have. (Expression of recessive
alleles or epistatically recessive genes is
non-additive.)
Narrow Sense proportion of phenotypic variance
due to additive genetic variance this is what
you have to work with if you want to improve
stock h2 VA/VP
In a parent-offspring regression analysis, r h2
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Hof, 1996
Williams, 2000
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Important things to know about heritability
1. Heritability does not indicate how much of a
trait is determined by genes. Heritability
deals with population variances. What if there
is no variance?
2. Individuals do not have heritability.

Heritability is a statistical measure of
population variances.
3. Heritability values are not universal or
stable.
Heritability depends on the
trait and the population.
4. High heritability does not mean environment
doesnt matter.
Heritability is
population dependent. If the current environment
of the population is not that variable, then most
of the variation in phenotype will not be due to
environmental variations.
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Response to Selection How do we use heritability?
Can I breed a fish stock that will gain weight
faster?
1. Determine that weight gain has significant
narrow-sense heritability. (parent-offspring
regression analyses experimental procedures
varying genotype and environment)
2. Preferential breeding truncation
experiments.
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