Ecology 3
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QG
quantitative genetics  the scientific study of the statistical analysis of the effects that heredity and environment have on phenotypic variation

2 ways to measure Darwin's step 4
 selection differential (s)
 selection gradient (B) "beta"

selection differential (s)
 describes the strength of selection relative to the distribution or variance of the phenotypic trait
 difference in mean phenotype between the population as a whole and the selected parents of the next generation

heritability
the proportion of phenotypic variation in a population that is attributable to genetic variation among individuals

selection gradient (B) "beta"
 the regression slope of "fitness" estimate on phenotype
 used more in ecological studies because it's easier to measure in the field

selection response (R)
the change in mean phenotype between parental generation before selection, and offspring generation (before selection on it, after selection on parental generation)

The breeder's equation
 R = h^{2} S
 R = V_{A }B"beta"

V_{A}
 additive genetic variance
 passed on from parents to offspring, as sum of 2 alleles effects, one from mom, one from dad

V_{P}
 total phenotypic variance
 S^{2} phenotypes
 V_{P} = V_{G} + V_{E}

narrow sense heritability
 h^{2 }= V_{A} / V_{P}
 h^{2} = 0,1, or inbetween, if so R<S

variance (V)
 measure of dispersion about a mean or average
 the standard deviation squared

V_{G}
 genetic variance
 V_{G} = V_{A} (additive) + V_{D} (dominance  interation between alleles within a gene) + V_{i} (interaction among genes, gene networks)
 **selection only responds to V_{A}
 _{}

V_{i}
 epistasis
 interaction among genes, gene networks

V_{e}
environmental variance

broad sense heritability
 H^{2} = V_{G} / V_{P}
 reflects all possible genetic contributions

locus (plural loci)
the specific location of a gene or DNA sequence on a chromosome