week 2 409
U of L
Popular in Evolutionary Biology
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This 2 page Class Notes was uploaded by Mary-elizabeth Notetaker on Thursday September 1, 2016. The Class Notes belongs to Bio 409 at University of Louisville taught by Jeffery Bara in Fall 2016. Since its upload, it has received 6 views. For similar materials see Evolutionary Biology in Biology at University of Louisville.
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Date Created: 09/01/16
Week 2 Monday, August 29, 2016 12:03 AM • Nat selection acts on phenotypes ○ Specific alleles/genes affect ability of orgs to be infected w virus ○ Environmentalconditions effect trait much more • Qualitative trait- discrete trait w easily identifiable states ○ Diff in phenotype explained by small # of loci • Quantitative trait- continuous distribution, no discrete classes ○ Affected by many genes and environmentalfactors ○ Usually bell shaped curve Mean Variance(variation about mean) □ Sum of all squared deviations of indivs about the mean • As loci increase, phenotypes begin to blend ○ Number of phenotypic classes when there are n diallelic additive loci is 2n+1 • Quantitative trait locus mapping(QTL)- studying relationship btwn marker(known chromosomal position) & phenotype ○ If marker is linked, would be associated w specific phenotype ○ No association=not linked ○ Where on the dna chromosome is trait loci- could be one or more loci • Candidate loci- to detect QTL look for association btwn marker genotype and phenotype ○ To identify QTL • Variability- understand entirety of heritable variation ○ Vp- characteristic of pop…measures spread around a mean ○ Vg- variation among indivs from gene diffs Vg=Va+Vd Va- additive genetic variability(codominantalleles)- responds easily to selection bc contribution of each allele constant across gens Vd- dominant genetic variability9recessive & dom alleles) □ Arises bs recessive allele contributes to phenotypic variability in homo but not hetero ○ Ve- variation among indivs from envir diffs ○ Distance squared is contribution of x2 to pop variance ○ Heritability(H^2)- proportion of Vp due to Vg Broad sense- always btwn 0 & 1: h^2=Vg/Vp □ Degree of genetic determination Narrow sense heritability: H^2=Va/Vp □ Predict how pop will survive bc shows how offspring resemble parents □ Slope of line describing relationship btwn midparent and midoffspring phenotype □ Any heritability estimate is specific to particular pop in certain envir • Quantifying portion of pop that survives/reproduces T- mean of all indivs t*- mean of breders Selection differential(S)- diff in trait's mean after and before selection S=t*-t • Response to selection(R)- expected change in trait mean from one gen to next from nat selection ○ R=O*-O O* actual trait mean of offspring gen(offspring of P*) O- mean of what offspring as whole, preselection parent gen P & O are same ○ R is less than S bc not all variation in quantitative traits is heritable ○ S= strength of selectionis = to diff btwn means of selected indivs and entire pop ○ Slope: R/S (still rise/run) ○ R=heritability x selective differential (h^2 x S) Estimating evolutionary trees pt 1: trees order the diversity of life ○ Slope: R/S (still rise/run) ○ R=heritability x selective differential (h^2 x S) Estimating evolutionary trees pt 1: trees order the diversity of life • Phylogenetics- evol of relationships among species and their descent from common ancestors • " trees- diagrams of evol history of a group of taxa ○ Clustering- based on physical proximity ○ Interpreting trees: Trait transitions- shown as bars on branches Cladograms- branch length doesn’t matter Shared(syn) trait unique(aut) Synapomorphy- homologies that help build trees Homoplasy- shared trait not reflecting common ancestry..arose independently in multiple lineages Causes: convergent evol reversions(genetictraits… regains ancestral trait from back mutation) Ancestral(plesio) derived(apo) Outgroup- close relative whose lineage branches off before your group of interest Det's whether a trait is most likely to be ancestral or derived Monophyletic(clades)- most recent commonancestor and its descendants Polphyletic- does not contain most recent commonancestor… not useful Paraphyletic- some but not all descendants from common ancestor Parsimony- simplest explanation most likely
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