ZOOL 4133 1st Edition Lecture 5 Mutation, migration, and drifI. What processes can cause changes in allele frequencies in a population? a. “no selection b. no mutationc. no migrationd. no genetic drifte. random mating”i. (list taken from lecture notes)II. By itself, mutation is a really weak evolutionary forceIII. Mutation and selectiona. Most new mutations are weakly deleterious i. reduces the relative fitness of individuals that carry them by a small amountii. most of the new mutations are not beneficialiii. progressively the fitness of the population declinesiv. selectionv. depending on population size1. deleterious alleles will be removedIV. Drosophila lab experimenta. regular table salt is lethal to fliesb. 5% salt diet kills all fliesc. 4% kills mostd. all flies are inbred for many generations (30 generations in total)i. experimenters varied salt concentrations; varying with generations1. 1%-6%ii. allowed for some individuals to survivee. utilized large population sizesi. each new gen 200 individualsii. allowed selection to operatef. results:i. eventually with 5% concentration, they got 3.5 flies surviving1. evident that selection happened - adaptive evolutiong. Why do a few individuals from unstressed lines survive?i. stress itself isn't what causes mutations1. not selected for, just by chance, it's there (the mutation)h. mutation just happens 'at a certain pace' "they click along at a constant pace"i. ^conclusion^V. mutation selection balancea. most new mutations are weakly deleteriousThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.b. in populations of sufficient size, deleterious mutations will be selected against andremoved from the population eventuallyc. why does genetic variance for these mutations persist? Why is there still variation in fitness in natural populations?i. mutation is constant ii. gives rise to new, unwanted allelesd. mutation-selection balancei. “conditions under which the mutation rate at a given locus 0 the strength of selection against deleterious alleles at that locus”ii. predicted frequency for a homozygote - lower probability of observing thehomozygous classiii. recessive deleterious allele1. q^2 = mew/s -->q=sqrt(mew/s)a. allows us to predict in relatively simple terms what the frequency of recessive deleterious alleles can beiv. dominant deleterious allele1. q=mew/s2. lethal dominant allelea. q=mewi. because anyone who has it is deade. with modern medicine, we are changing the frequency in which these deleterious alleles occur in the populationi. we are kind of artificially selecting ourselvesVI. Migrationa. "the movement of alleles between populations"b. it is not the seasonal movement of individuals between geographic areasi. ecological definitionii. this doesn't change allele frequencies c. how does migration change frequencies within a population?d. mice experimenti. locus A1 is fixed1. frequency = 1ii. A21. not there in the populationiii. 800 mice zygotes mature1. genotypes frequency stay the sameiv. immigrants come in (200 individuals)1. homozygous for A2 allele2. join first populationa. allele frequency changes without any interbreedingv. final allele freq = .8 and .21. expectede. What are the main consequences of the movement of alleles between pops?i. increases frequencies in the population1. allelic diversityii. homogenation of allele frequencies between populationsiii. populations determined by amount of gene flowf. "if a pop is locally adapted, selection can oppose the homogenizing effect of gene flow"VII. Lake Erie water snake examplea. trait controlled by single gene b. banded phenotype Genetic driftI. Mutation is a random process that allows new alleles to arise in each generation at a constant ratea. adds allele variation, changes allele frequency at a steady rateb. selection is non-random process that acts upon existing, as well as, new alleles that affect individual fitnessc. “changes allele frequencies at the locus under selection”d. genetic drift is a random process that results in changes in allele frequencies across generationse. mutation changes allele rates genome-wideII. starting allele frequenciesa. A1=0.6 A2 = 0.4b. random mating producesi. 10 zygotesii. random process of pulling out these allelesc. in very small populations, genetic drift is a very strong evolutionary forced. genetic drift in nature as shown by founder effectse. when a small number of individuals go and colonize a new environment i. often an islandIII. Polynesian crickets examplea. originally from Australia, New Guinea i. end up with a reduction in genetic diversityii. true for whole genome because it's a random process1. “genetic drift has a faster, nor dramatic effect in small populations2. because drift is a random process, every pop follows a unique path3. given enough time, drift can cause substantial changes in allele frequencies, even in large pops4. in absence of other evolutionary forces, drift causes the eventual fixation of some alleles and loss of others5. as alleles drift to fixation heterozygotes in the population declines”(1-5 taken from