Quantitative Genetics Flashcards
What are some qualities of qualitative traits?
-discrete phenotypic classes
-discontinuous variation in F2
What are some qualities of quantitative traits?
-continuous variation
-no distinct F2 classes
What is the multiple-factor hypothesis?
phenotypic expression depends on additive effects, as the number of loci affecting the trait increases so does the number of phenotypic classes
Variation can be due to
genotype and the environment
Continuous variation is when
the characteristics exhibited cover a continuous range of phenotypes
A “normal distribution” is…
a bell-shaped curve.
What are the different components of phenotypic variance?
Genotypic Variance, Vg
Environmental Variance, Ve
Additive Genetic Variance, Va
Dominance Genetic Variance, Vd
Phenotypic variance equation
Phenotypic variance = Genetic variance (genotype) + environmental variance
Genotypic variance equation
Genetic variance=Additive genetic variance + dominance genetic variance
To determine phenotype and genotype equation values you must look at the
population
The effect of the gene depends on the…
environment in which it is found
Interactions that we will ignore are…
Vge is a part of the Vp equation
Vi is a part of the Vg equation
Heritability is used to
tell the rate of selection response in a breeding program
Broad-sense heritability is the…
phenotypic variance due to some genetic effect
Broad-sense heritability equation
H^2=Vg/Vp
Narrow-sense heritability is the…
phenotypic variance due to additive genetic effects
Narrow-sense heritability equation
h^2=Va/Vp
h^2=R/S
Heritability ranges from 0 to 1. If it equals 0 then ____________, if it equals 1 then __________.
all Vp is due to environmental variation, all Vp is due to genetic variation
The higher the heritability the…
more progress we can expect from a selection/breeding program
Environmental variance equation
(Vparent1 + Vparent 2 + Vf1)/3
Response to selection is
the extent to which the characteristic changes over a generation
Selection differential (S) equation
S = Xs -Xo
S = (average new breed) - (original average)
Response to selection (R) equation
R = X1 - Xo
R =(average of offspring) - (average original)
Realized heritability equation
h^2=R/S
Limits to selection response
-may decline after selecting a particular characteristic in a population for a long period
-due to genetic variation being lost
-extremes may not be healthy
-two desirable traits may be negatively correlated
How are quantitative trait loci mapped using GWAS?
They are identified by linkage analysis between the trait and molecular markers. SNPs are used to identify QTL
In GWAS anything above the line is
statistically different
Limitations to heritability
-doesn’t say how much genes affect the trait
-individuals don’t have heritability
Monozygotic vs Dizygotic Twins
-Monozygotic: genetically identical same womb
-Dizygotic: only 50% of genetics shared, different wombs
Concordant vs Discordant
Concordant: twins same for traits
Discordant: twins differ in trait
Twin studies can be used to estimate what?
genetic and environmental influences on traits
When MZ ratio is high & DZ ratio is low…
Indicates significant role of genetic effects
Similar MZ & DZ indicates…
a lot of variation due to environmental factors
When MZ ratio is low & DZ ratio is high…
indicates genetic predisposition, but environmental factors are important
