week 6 409 & quiz 2 correct answers
week 6 409 & quiz 2 correct answers Bio 409
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This 7 page Class Notes was uploaded by Mary-elizabeth Notetaker on Thursday September 29, 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 2 views. For similar materials see Evolutionary Biology in Biology at University of Louisville.
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Date Created: 09/29/16
Week 6 Tuesday, September 27, 2016 2:24 PM Selection- diff survival/reprod due to genetics ○ Even small fitness diffs can lead to substantial change in allele freq across gens 4 postulates of NS are independently verifiable & testable ○ Ex) is fish body size evolving by NS phenotypic variation due to diff alleles/allelecombos Phenotype heritable(genetics) If survival/reprod nonrandom w respect to phenotypic variation allele freqs will change across gens ○ Selection and rate of change allele freq: principles Rate of fixation of alleles is proportional to strength of selection on them □ Strong when diff alleles, weak when alleles closely resemble each other Allele changes due to selection are repeatable and deterministic in infinite pop Given allele freqs & fitness of genotype, can predict allele freq changes across gen 1. Predicting changes in allele freqs due to selection 2 2 i. If in HW know allele freqs from p 2pq q 2. Generate breeding adults i. At t=0(start of life cycle), have genotypes and fitness of each genotype ii. Get relative fitness for whole pop: Relative fitness more imp than absolute fitness bc: selection only occurs when there are diffs Relative- how fit compared to each other w/in pop Will inc in freq… dependent on envir conds Predicting changes in allele freq due to selection Bio 409 Page 1 Cavener & clegg- lab evidence for NS using fruit fly 1 diet w ethanol, 1 without.. Monitored ADH allele freq ADHf(breaks down alcohol dehydrogenase faster than ADHs) inc in freq in pop selected for better ethanol metabolism … drift keeps curves from looking like theoreticals Drift & selection- ecol forces not mutualluy exclusive Much stronger in smaller pops w/NS: Prob of fixing alone is 1/2N To the extent which selection improves/impares alleles chance of fixation det'd by formula: 2N e Ne= effective pop size S= differential measure of fitness ..larger= inc prob that allele will fix Clonal interference- beneficial mutations(alleles) competing to fixation Beneficial mutations w higher fitness effects tend to be fixed Ex) HWE in action Outcome of placental malaria influenced by fetus's genotype at locus encoding (VEGFR1)- 2 alleles; S & L SS & SL produce more than LL When malaria rate low: 55% had S,44% had L… if in HW: SS= 55^2=3,025 0.308 SL=2 x 0.55 x 0.445=0.2448 0.494 LL=0.445^2=0.198 Actual were very close to theoretical When high: S=0.539, L=0.461 This time actual were off from theoretical …homos likely did not survive fetal development Types of phenotypic variation: Genetically caused variation Envir " " Variation arising thru genotype-by-envir intxs Selection on dom & recessive alleles 2 alleles… + & l Collected heteros & estbl 2 experimental pops Selection against l/l is rapid initial but slows A1 common, most in homo A1 at intermed, half in homo, half in hetero A1 rare, most in heteros Recessively inherited diseases: CF, Tay-Sachs, muscular dystrophy Read 6.3 about changing allele freq from selection ○ Mult freq x fitness of each allele and divideby avg fitness to get freq after selecdtion which will show how allele changing If inc, being selected for Bio 409 Page 2 will show how allele changing If inc, being selected for If dec, being selected against(deleterious ) Selection on recessive allele(against)- fit of homo will be relatively lower Selection on dom alleles (against) Ex) Many will have aa geno and if they have lower fitness relative to AA or Aa then freq of a is going to dec in next gen from selection As selection continues to act against aa geno, majority of a alleles will be found in Aa and will be shielded from selection (so will be maintained in pop) Selection against recessive is selection for dom, and vice versa Rapidly at first then slows as majority of alleles become shielded If selection coeff is .5 then fitness =1-.5 Selection favoring heteros: Ex) selection for/against recessive/dom alleles Hetero beetle pop + allele, l allele ….. Ll died All indiv started as +l V allele is viable, l is lethal Estbl pop and let gens go for 15 yrs Freq of viable allele started at .5, jumped to .7..would expect freq to be at .95 but settles at .79 … bc lethal allele was shielded in heteros in pop ..hetero superiority- when hetero is higher fitness than either homo Tested by redoing exp starting w almost all indivshomo for V allele, let pops evolve…over time still settled in at .79 so proved VV lower fitness than VL -Where eq is depends on fitness diff btwn hetero and homo …mech to maintain polymorphism in pops (diversity) Fate of all alleles is fixation or loss Bio 409 Page 3 Fate of all alleles is fixation or loss Evidence for hetero advantage selection: Humans… SCA: AA susceptible to malaria Aa resistant to maleria, only mild SCD (most fit..depending on envir) Aa resistant to maleria but has fatal SCD CF… Homo susceptible to typhoid fever causing bacterium Hetero more resistant Homo recessive very resistant but has CF Explaining persistence of genetic disorders: 1. Hetero adv.. Can maintain alleles deleterious in homos 2. NS is in process of removing them but needs more time 3. Mut-selection balance… mut constantly occurring and selection constantly acting on them 4. Timing of selection a. Strength of selection powerful before indiv reproduce, genetic disorders that appear later in life may not affect fitness 5. Can be maintained by gene flow- allele mut not be deleterious in envir/pop from which the indiv came Could be deleterious if moved btwn envir/pops Typically recessively inherited diseases are selected against Predominantly inherited diseases (huntingtins)section has nothing to act on bc indivs have already reproduces Evol of mult loci: linkage and sex Concerned w allele freq and chromosome freq 4 possiblegenotypes now Aa, Bb, AB, ab Multilocus genotype of chromosome known as haplotype Rate of crossover depends on how closethey are Closer on same chrom= more physicallylinked in crossing over Linkage disequilibrium-pops can have ID allele freqs but diff chrom freqs, which can influence evol 1. Calc allele freq (A a B b) 2. Calc chrom freq (AB Ab aB ab) .. Get linkage diseq if AB aB freq not equal, or if Ab ab freq not same B bearing chromosomes v b " " Two loci in eq when genotype at one locus is indep of another locus " " in diseq when nonrandom assoc btwn geno at one locus and geno at another locus Conds of linkage eq: 1. Freq of B on chrom w A allele is = to freq of B on chrom w a allele 2. Freq of haplotype can be calc'd by mult freqs on 2 alleles 3. Coeff of linkage diseq =0 Mech that drive linkage diseq: Bio 409 Page 4 Mech that drive linkage diseq: 1. Multi locus selection causes LD Quantitative traits.. Mult loci contributing to animal size A/B contribute to body size Predation such that only animals w at least 3 capital letters will survivebc too large for predation Epistasis- affect of one allele/gene depends on what other alleles present AA- always have 3 big alleles Aa- maybe .. Depends on other B allele Aa- will not make cutoff so will not survive … so indiv that survive are in LD(violate all 3 conds to LE) 2. Genetic drift a. Starting pop w LE i. Copies of a do not exist ii. Mutation arises for one ab geno 1) No aB geno so in LD but couldn’t det in nature iii. If selection favors ab geno … in infinite pop, every possiblemut will occur on every chrom .. In finite pop, sampling error(drift/randomness) leads to mutation showing up once and in AB chrom 3. Pop admixture- gene flow a. 2 diff gene pops… have migration in gene pool b. 2 previously indep pops come together.. Depending on allele freqs can cause LD when pops first come together LD eliminated from pop by sexual reprod and random mating Empirical data suggest that sex reduces LD Started at complete LD.. Allow random mating over time.. Merge to state of LE Conseq of LD: Selection at one loci can change allele freq at another loci that isnt under selection Bc linked to the other loci Genetic hitchhicking- can get beneficial mutation and smaller deleterious muts.. Deleterious can be swept to fixation bc linked to larger beneficial mutation Bio 409 Page 5 Quiz 2 review Thursday, September 29, 2016 2:30 PM -NTK how 5forces of evol act to influence allele freqs Read ch 6 & 7 and mutation in ch5, & first part of ch 8 Test will be in depth Migration- gene flow btwn pops Anything that moves alleles from one pop to another Dispersal of juvenile animals Homogenizing effetc, island model Genetic drift- differential reproductive success by chance and not fitness Founder effect- likely that chance alone will cause allele freqs in new pop found by small # of indiv to be diff than source pop Allele freq in new pop different than source pop Mutation is how new genetic variation arises… ultimate source of all genetic variation Non random mating(inbreeding) affects genotype but not allele freqs Inbreeding- mating among genetic relatives… inc freq of homos compared to expected freq under HWE 1. 2. A=.65 a2=? 400 indivs… freqs? P2=0.65 x 0.65 1-.65=.35 2pq=2(0.65 x 0.35) Q2= 0.35 x 0.35 .65 x .65 = 0.4225 .35 x .65=0.2275 .2275 + .2275=0.455 .445 + .4225=0.8675 , so q2= .1225 4. In a, lethal muts & deleterious most common, then neutral, then beneficial 4. In a, lethal muts & deleterious most common, then neutral, then beneficial In b, neutral most common, then deleterious, then beneficial A & b diff bc don’t observe lethal muts in nature A & b diff bc selection purges lethal muts from pop & shifts proportion of observed muts..commonly observed fitness effect of mut was neutral ..rel freq based on selection 3. a) Mol change conserv in nature bc mol change more likely to happen in genome areas that don’t effect fitness Accumulate in psueudogenes bc don’t affect fitness..evolve faster Syn sites evolve faster than nonsyn sites Less locus affects phenotype, more common is variation and sub b) Mol change is constant bc fixation rate=mut rate Indep of pop size and envir Rate of fixation in pop= mut rate… mut rate usually similar and constant in clock like fashion regardless of size Sub rate=mut rate regardless of pop size