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30 Cards in this Set
- Front
- Back
- 3rd side (hint)
What's the major differences between quantitative genetics and single-locus models? |
Quant gen depends on many genes & are affected by the environment. Are more closely linked to fitness, but are harder to estimate the gen var. |
Four diffs |
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What's studied in quant gen? What describes the different 'study subjects'? |
1. Continuous traits. Described with mean & variance/standard deviation 2. Meristic traits, integers. Described with the parameter λ (variance=mean) 3. Threshold traits, discrete. The underlying genetic variation is continuously distributed. |
Three types of traits |
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Which are the components of phenotypic variation? |
Vp=Vg+Ve |
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What does Ve include? And Vg? |
Ve: The direct effect of environment and developmental noise Vg=Va+Vd+Vi (additive, dominance, epistasis/interaction var) |
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What's the formula for broad-sense and narrow-sense heritability? |
Hb=Vg/(Vg+Ve) Hn=Va/Vp (Here Vp=Va+Ve) |
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What heritability measurement is preferably used to predict response to selection, and why? |
Narrow-sense, since broad-sense includes epistasis effects and these can cause gen var to not be expressed in phenotype - phenotype is that which is measured to predict the response. |
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Can heritability measurement for a trait be generalized to be the same under all conditions? Motivate. |
No, since heritability depends on environment, the value depends on the conditions and may differ |
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What's "additive effect", how is it calculated? What factor affects the additive effect? |
a=The effect of the different alleles in a heterozygote genotype, it equals half the difference between the homozygotes' mean phenotype values a=(a1-a2)/2 Is affected by dominance, which is calculated by sustracting the observed value of heterozygotes from the expected value of heterozygotes (The expected value of heteroz=(one of the) measured homoz value minus the additive effect) |
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How can heritability be estimated? |
1. Parent offspring regression: the regression slope equals the heritability (Hn). If only one parent is known/measured - Hn=2*the slope 2. Progeny testing "sire model": phenotypic similarity in full- & half-sibs. Vf=pheno. var. AMONG families. For half-sibs Va=4Vf --> Hn=4Vf/Vp 3. Animal model: when it's hard to minimize or measure Ve - use pedigree info and individual phenotypes to estimate Va and Ve with statistical ML model |
Three diff methods |
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What component can be included in Vp apart from the usual two? |
V(g*e), there can be interactions between genotype and environment --> different performence of genotypes depending on the environment |
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What's the definition of local adaptation? |
A local population that has greater fitness in their native habitat is locally adapted |
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What equation can measure directional selection? |
"Breeders equation": R=Hn*S S is the selection differential R is the response to selection |
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What factors affects Va (what does Va depend on)? |
It depends on Ve, but can also depend on allele frequency ONLY IF there's a dominance effect |
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What do we need to know to calculate the additive effect for each allele? Why would we want to calculate this (what can it be used for)? |
The fitness of the genotypes (and genotype frequency) This can be used to calculate the additive effect in the genotypes, i.e. Va |
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What causes genetic correlation? |
Pleiotropy or linkage disequilibrium |
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How can genetically correlated traits be affected by selection, i.e. what happens if there's selection for only one of the traits? |
Two possible outcomes: 1. Both traits will increase in fitness 2. One trait increase in fitness, the other decrease: a trade-off, this constrains selection |
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How can we find genes affecting quantitative traits? |
1. QTL mapping 2. Candidate gene approach 3. Genome-wide association mapping (GWAS) |
Three diff methods |
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What is QTL? How do you identify a QTL? |
A region of the genome containing one or more genes that affect variation in a quant trait. Identified by its linkage to polymorphic marker loci through analysis of phenotypes and marker genotypes in F2 generation (P: homozygous for markers, F1: intermediate, cross F1xF1 or F1xP) |
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How is GWAS performed? |
Genome-wide associations: Very many markers across the genome are genotyped randomly, looking for associations between allelic variation & phenotypic trait of interest. |
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What makes GWAS so expensive? |
Huge sample size is needed since there's lots of variation in a genome and we can't control the environmental effects when not doing experiments (but taking samples from wild pops) |
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What may cause loss of variation in quant traits? |
Genetic drift or selection (fixation of beneficial alleles) |
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Can variation in neutral markers predict quant gen variation? |
There's a low correlation between heritability (Hn) and pop size (in the wild), we can't easily use neutral markers for predictions of quant gen var: only general predictions, no clear correlations. |
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Why can variation persist in highly polygenic traits even under strong selection? |
1. Low initial freqs of sel alleles 2. Epistatic effects 3. New mutations (when there's many genes involved, it's more probable a mutation will appear & affect the trait) 4. Change in environment |
Four reasons |
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What's Qst? |
A measurement of divergence between pops, Qst=Va between pops/(2*within pop+between pop) |
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How do you interpret these results: Qst>FST Qst=FST Qst<FST? |
Qst>FST - differential directional selection on quant trait Qst=FST - Amount of diff at quant trait similar to expected by gen drift Qst<FST - Natural sel favouring the same phenotype in different pops |
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For what can quant var be used in a common garden experiment (with plants)? |
To identify source pop for restoration & to estimate adaptability to environmental changes |
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Why is quant variation/genetics useful for conservation of animals? |
Progress is likely to come from identification of genes affecting quant traits |
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Does quantitative traits correlate with variation and pop divergence estimates? |
Sometimes they do, sometimes they don't! |
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What experiment could be performed if we want to study if a antipredator behaviour is inherited or taugth? Motivate. |
Cross-fostering (with long-term observations), then do a regression analysis between offspring-biological midparent, and offspring-foster midparent. This type of study allow separation of genetic effects and environmental effects including maternal effects within a natural environment (in naturalpopulations, genetic effects are confounded with environmental effects whenparents raise their own offspring). |
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The slope of theregression of progeny vertebrae number on maternal vertebrae number in velvetbelly sharks is 0,42. Whatis the estimated narrow-sense heritability for this trait? |
HN = 0.84(HN = 2 x slope of regression when phenotype for only one parent isknown) |
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