Evo

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evo by ns requires 3 things

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1 variation in traits among individuals w/in a pop

2 reproductive success varies with traits

3 traits are heritable

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Natural Selection

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differential survival and/or reproduction of individuals resulting from differences in the inherited traits they possess

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Evolutionary response to selection

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genetic changes in populations that result from the process of selection

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consistent with natural selection v demonstrate adaptive evolution

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cases

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natural selection without evo

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natural selectionmaintains the status quo by eliminating deviants from the optimal phenotype

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evo without natural selection

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drift (neutral), selective evo

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neutral evolution (evo by genetic drift) if:

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variation in heritable traits and

variation in reproduction BUT no correlation between the two

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ways to empirically assess whether adaptive evo has occured

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phenotypic approaches (pheno/fitness correlation, pheno + fitness over time comparative approach, selection experiments, trait function/fitness experiments, theoretical modeling) and genotypic approaches (same but with genetic, analysis of signals of selection within genomes)

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Macroevolutionary patterns???

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explain?

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for each lecture 2 slide

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be able to do slide 2

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adaptation

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state or trait that evolved because it improved relative lifetime reproductive success; also the process that produces that state or trait

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adaptive evolution

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process of change in pop driven by variation in reproductive success that is correlated with heritable variation in a trait

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difference between natural selection and adaptive evolution

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?

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difference in action of selection and response to selection

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response is shift genotypical while action is centered on phenotype

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survival of the fittest is poor metaphor for natural selection

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reproduction of the fittest...

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TorF: natural selection favors traits that will benefit a species the most

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F: it doesn't "favor", natural selection?

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what does "evolution is not progressive" mean?

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?

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genetic drift

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random change in allele frequencies due to chance factors; occurs because of "sampling errors"

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mendelian lottery effects in different pop size

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small = strong effects

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genetic drift reduces genetic variation __ pops but increases genetic variation __ pops

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within, among; genetic drift fixates on a certain allele that decreases genetic variation IN a pop but fixation may be different in different pops thus increasing genetic variation BETWEEN pops

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pop size v fixation rate

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small pop = fast fixation rate, large pop = slow fixation rate

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probability of fixation of a new allele (substitution)

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= 1/(2N)

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probability of new mutation being lost

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= 1 -1/(2N)

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2 demographic processes that enhance the effects of drift via effects on pop size

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genetic bottleneck, founder effects

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genetic bottleneck

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pop is dramatically reduced in size, leaving a different freq of alleles

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founder effects

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a small subset of a population starts a new pop elsewhere; over multiple colonizations allelic diversity decreases (most different= original and newest colony, most alike= time sequential)

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island size (after genetic bottleneck event) v diversity

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size (certain alleles knocked out) genetic diversity low on small islands (1/(2N)

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genotype effect on fitness

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genes > proteins > phenotype > fitness

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redundancy

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example of redundancy

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12 replicate colonies from single close (E.coli), each pop propagated for generations in identical enviros, pops test for fitness by "competing against each other; results - each pop improved fitness by avg 35% relative to parent clone, but variability in fitness among pops very low 2-3%; conclusion - each pop evolved to common final fitness state; explanations - 1) all pop experienced same genetic changes -> same pheno changes or 2) pops varied in genetic changes but various geno produced similar pheno w similar fitness (THIS one if pops subsequently tested on different media and a lot of variation... ADAPTIVE)

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Neutral Theory of Molecular Evolution

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most of the OBSERVED variation in DNA sequences is due to drift instead of selection (degenerate genetic code: amino acids coded for by several different codons / synonymous mutation / lots of substitution in less rigid 3rd position)

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Viral example of synonymous mutations and drift

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less non-synonymous mutations over the years bc prob would die out?... thus synonymous mutations much more responsible for observed variation in DNA sequences

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how can a new function evolve via drift

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original sequence of functional genes along chrom -> a gene is duplicated -> original gene maintains function but duplicated copy is free to drift -> could eventually evolve a new function

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evolutionary consequence of drift (complexity v pop size)

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increasing population size results in less complexity = deficiencies in protein structure more likely to be retained in smaller pops -> leads to stronger selection for protein-protein complexes that compensate for deficiencies

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gene, locus, allele

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gene- functional unit of DNA coding for pheno

locus- refers to specific region of chrom where gene is

allele- variant form of gene

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Hardy-Weinberg Model

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genotype and allele freq in pops that are not evolving, shows allele freqs constant across gens unless acted upon by some outside force, pop not evolving is at "H-W equilibrium" , p^2 + 2pq + q^2 = 1

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factors that cause deviation from H-W eq

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genetic changes (mutation), genetic drift (random events affect allele freqs), non-random mating (preferences, social dom), gene flow among pops (migration - exchange of alleles), natural selection

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asexual haploid frequency equations

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p'=p/(1-sq) or p(1)/(p(1) + q(1-s))

q'=q(1-sq)/(1-sq) q(1-s)/(p(1) + q(1-s))

numerator: fraction of original allele freq remaining after selection

denominator: sums new allele freqs after selection

allele freq remaining after s/ total new sum freqs

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sexual diploid freq equations

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A1A1 = p^2(1)/W

A1A2 = 2pq(1-hs)/W

A2A2 = q^2(1-s)/W

p'= (p^2 + pq(1-hs))/W

q'= (q^2 + pq(1-hs))/W

W= p^2 + 2pq(1-hs) + q^2(1-s)

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strength of selection v rate of fixation

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(assuming A1 is dominant, advantageous) higher s = faster rate of fixation

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dominance v rate of fixation

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dominant = quicker increase towards fixation but longer to actually reach 1

recessive = slower to increase towards fixation but quicker to reach 1

(with dominant, recessive allele can "hide" in heterozygotes so takes longer to reach actual fixation while with recessive the alleles can stay at low freq even if they have fitness advantage)

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what shape are all the lines on a freq of new allele v generation plot? and what does this mean?

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sigmoid (s-shaped), indicates that rate of evolutionary change is greatest at intermediate allele frequencies WHY? when freq is low it is slower to spread bc less individuals can pass on and when freq is high most individuals have it so not much change when passed on BUT when freq is intermediate the alleles are rapidly passed on?

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population genetics v quantitative genetics

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pop: each trait has one antecedent locus

quant: each trait has many antecedent locus (each with many alleles)

HOW do they respond differently?

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quantitative genetics

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focuses on causes of changes in TRAITS rather than in allele freqs, geno and enviro effects on enviro, focuses on means and variances of quantitative characters, uses amount of Vg and its h2 to predict how character will change under selection, deals with continuous phenotypes (due to both genetic and phenotypic variation)

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prob an allele will reach fixation =

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freq in pop (if allele A freq= 20% then 20% chance of reaching fixation- but simplified)

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experiment to understand Ve versus Vg

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Ve: clones/twins in diff enviro (cuttings of plant put in different elevations = diff height)

Vg: offspring in same enviro (plants w diff geno put at same elevation/enviro = diff height)

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types of continuous phenotype

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multiple loci w two alleles or a single locus with multiple alleles are all additive

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variance

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= summation (i=1 to N) of (Xi - Xmean)^2/ (N-1)

The average of the squared differences from the Mean

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what is limiting about broad sense heritability

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H^2= Vg/Vp: accounts for genetic material that doesn't influence Vp (junk DNA, synonymous differences, if 3 geno give rise to 2 pheno in dominance situation) and some Vg doesnt respond to selection (if heterozygotes are favored over either homo)

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narrow sense heritability

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Vg = Va + Vd + Vi -> h^2= Va/ Va + Vd + Vi +Ve

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high additive genetic variance

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each allele contributes to pheno, each geno gives rise to unique pheno (under constant enviro)

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why is h^2 useful

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bc it measures the expected response to selection: greater Va the greater potential to respond to selection

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Selection differential and response

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S= Us - U

R= U' - U

h^2= R/S

R= S*h^2 = S*(Va/Vp)

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what does a slope of midparent value v midoffspring value equate to

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heritability

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additive genetic variance

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component of genetic variance in a character that is attributable to additive effects of alleles

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why is heritability h "^2"

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derives from when h was used as corresponding ratio of standard deviations

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selection coefficient

differential

intensity

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s -> measure of the relative reduction in the contribution a particular genotype makes to the gametes (sex cells) compared with another genotype in pop. It expresses the relative advantage or disadvantage of specific traits with respect to survival and reproductive success.

S -> to measure s in field: difference of base pop mean and selected parent mean (R is difference of trait in base pop and in offspring of selected pop)

i= S/sqrtVariance: proportion of the phenotypic trait that has changed

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selection gradient

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strength of selection on single trait, independent of selection on correlated traits (slope of trait v fitness graph regression line)

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genetic correlations affect response to selection

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can decouple response to NS from act of NS

ex: increase height = increase in mass, positive and negative correlations (resource acquisition towards maintenance/survival/growth or reproduction), may slow rate of adaptation: resistance?, snakes like certain shapes but leeches bad slugs good...trade off

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what would disrupt genetic correlations

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new gene arising

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what can decouple the act from the response of selection

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developmental processes (pheno plastic) and genetic correlations

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phenotypic plasticity

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ability of genotype to respond variably under different enviro conditions (helmets)

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induced response

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single geno produces a diff pheno in response to specific enviros

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reaction norm

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describes range of phenos that can be produced by a genotype under different enviro conditions (bundle of rxn norms= reaction norms of multiple genos)

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test pheno plasticity

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clones in different enviros (not just species individuals because don't want multiple genotypes or rxn norms getting in way)

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S v B

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Theselection differential (S; ms- m) depicts the netchange in a trait due to selection: Thatis, it includes both directselection on the focal trait and indirectselection on correlated traits that thereby also causes change in the focaltrait.

Theselection gradient (the slope, β, of fitness regressed on atrait) represents the strength of direct selection on a trait, independent of selection on other traits.

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Bird paper h^2*S=R

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