BIO2008: Lecture 7

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  • Created by: LMoney
  • Created on: 11-05-14 12:19
How are quantitative traits measured?
Measured as change of mean and distribution, not allele frequencies- focuses on causes of change in traits rather than on the causes of change in genes- NOT traditional population genetics that is concentrated on allele-frequencies and their changes
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In a homogeneous population, e.g. clones, variation is caused only by what?
The environment
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what is the effect environment?
a single genotype will not always have exactly same phenotype
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quantative traits are based on variation at many loci what does this mean?
generally spread all over genome, each with small effect
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what are the effects of genetic variation at each of those loci?
1) additive effects 2) dominance effects 3) interaction (between genes)
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(to reiterate) what must also be taken into account in quantative traits?
the environment
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what does VP = VG + VE mean?
Phenotype is the sum of genotype and the effect of the environment: Same phenotype not necessarily same genotype and vice versa
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what do Vp, VG and VE mean?
VP total variance between phenotypes VG variance due to genetic effects VE variance due to environmental effects
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what is plasticity? (phenotypic plasticity)
Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment.
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what is an example of phenotypic plasticity?
water buttercups (Ranunculus aquatilis) leaf shape changes completely in the water
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which organism provides a good example of gender differences AND genotype/environment interaction?
the map butterfly
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what can VG be split into?
- VA variance due to additive genetic effects - VD variance due to dominance genetic effects - VI variance due to the interaction genetic effects
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what does this change the equation into thereafter?
VP = VA + VD + VI +VE
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how can we quantify how much variation is genetic?
heritability- Fraction of variation between individuals that is due to their genotypes- written as h^2
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another definition of heritability?
Contribution of genetic variation to the phenotypic variation- heritability is between 0 and 1
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what does it mean if heritability is 0 or 1?
0: all variation is environmental effect 1: all variation due to genes (never)
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what is broad senesce heritability?
VG / VP (H^2)
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what is narrow sense heritability?
VA / VP (h^2)
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how do you measure heritability?
1) Selection: the effect of selection over generations Artificial selection Natural selection: effect in natural populations 2) Parent offspring regression 3) Similarity of related individuals
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What if you do not have result of selection lines or parent – offspring regression?
Use similarity of phenotypes between relatives Similarity of identical twins Similarity of ‘brothers and sisters’
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how is similarity of related individuals ascertained?
ANOVA
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Card 2

Front

In a homogeneous population, e.g. clones, variation is caused only by what?

Back

The environment

Card 3

Front

what is the effect environment?

Back

Preview of the front of card 3

Card 4

Front

quantative traits are based on variation at many loci what does this mean?

Back

Preview of the front of card 4

Card 5

Front

what are the effects of genetic variation at each of those loci?

Back

Preview of the front of card 5
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