What you need to be able to do for Exam 2 Chapter 6 Lectures 6 and 7 Be able to use the equation for selection in haploids to predict genetic change in the next generation Selection in haploid organisms A locus has two alleles A1 and A2 Each allele has a frequency p and q 1 p Each allele has an associated fitness W1 and W2 How will the allele frequencies change What is meant by fitness Fitness allows you to see what is happening in frequencies rather than absolute numbers Removes potential confusion of population increase or decrease Can scale by population mean fitness OR set one of the alleles as having fitness of 1 and scale the other appropriately W absolute fitness number of progeny in a generation assuming non overlapping generations So for example N1 N1W1 Using same logic q qw2 wbar Selection coefficient s w1 w2 p N1 N1 N2 N1W1 N1W1 N2W2 pw1 bar Change in allele frequency p p p p w1 wbar bar Change in allele frequency is equal to the final allele frequency minus the initial bar mean fitness in the population Be able to estimate allele frequencies from genotype frequencies Example a population with genotype frequencies of 0 36 AA 0 48 Aa and 0 16 aa Given genotype frequencies use the following equations to estimate the frequency of the A and a alleles Freq A F AA 0 5F Aa 0 6 Freq a F aa 0 5F Aa 0 4 Be able to calculate allele frequencies from phenotype frequencies for a population in Hardy Weinberg equilibrium Here is an example that I found online for the question It shows the genotype frequencies given and how to convert them to allelic frequencies It is important to remember that p and q represent the dominant and recessive alleles respectively for a trait Also that in HW equilibrium homozygous dominant genotype is represented by p2 heterozygous genotype is 2pq and homozygous recessive is q2 1 A study on blood types in a population found the following genotypic distribution among the people sampled 1101 were MM 1496 were MN and 503 were NN Calculate the allele frequencies of M and N the expected numbers of the three genotypic classes assuming random mating Using X2 determine whether or not this population is in Hardy Weinberg equilibrium OBSERVED GENOTYPE FREQUENCIES MM p2 1101 3100 0 356 MN 2pq 1496 3100 0 482 NN q2 503 3100 0 162 ALLELE FREQUENCIES Freq of M p p2 1 2 2pq 0 356 1 2 0 482 0 356 0 241 0 597 Freq of N q 1 p 1 0 597 0 403 Be able to test a population given genotype frequencies to see if it is in Hardy Weinberg equilibrium using a chi square test The next step in the equation above is to convert the OBSERVED genotype frequencies into the EXPECTED genotype frequencies or expected frequencies of the individuals assuming HW equilibrium This is done by taking the allele frequencies calculated above and plugging them in as we talked about before We must calculate p2 2pq and q2 which all represent the genotypes that we are measuring Once we are done with this we will be able to use the chi square equation and actually see if a population is in HW equilibrium or not EXPECTED GENOTYPE FREQUENCIES assuming Hardy Weinberg MM p2 0 597 2 0 357 MN 2pq 2 0 597 0 403 0 481 NN q2 0 403 2 0 162 EXPECTED NUMBER OF INDIVIDUALS of EACH GENOTYPE MM 0 357 X 3100 1107 MN 0 481 X 3100 1491 NN 0 162 X 3100 502 CHI SQUARE X2 X2 Observed genotype Expected genotype 2 Expected genotype X2 1101 1107 2 1107 1496 1491 2 1491 502 503 2 503 6 2 1107 5 2 1491 1 2 503 0 0325 0 0168 0 002 0 0513 X2 calculated X2 table 3 841 1 df 0 05 ls Therefore conclude that there is no statistically significant difference between what you observed and what you expected under Hardy Weinberg That is you fail to reject the null hypothesis and conclude that the population is in HWE Be able to use the equation for selection in diploids to predict genetic change in the next generation Modeling selection in diploid organisms Assign fitnesses to genotypes rather than alleles One locus selection diploids Two alleles A1 A2 p frequency of A1 q frequency of A2 p2 frequency of A1A1 genotype etc Fitnesses Genotype A1A1 A1A2 A2A2 Relative Fitness w11 w12 w22 p p2 11 pq 12 bar p 1 bar Where 1 p 11 q 12 WHY Dp p p p 1 bar bar Be able to calculate changes in allele frequency due to mutation Model of mutation p p p rate of mutation from p allele to q allele q q p After n generations pn p0e n Be able to calculate the equilibrium frequency due to mutation selection balance Mutation selection balance mutation is adding variation at the same rate that selection is taking it out Why is there so much genetic variation within natural populations One way that this can happen is through mutation selection balance Say that we have a recessive deleterious allele o 22 1 s Fitnesses of other genotypes 1 System with selection followed by mutation From last lecture p p following selection but before mutation p p 1 s 1 p 2 p 1 p 1 p 1 s 1 p 2 Now we add mutation At equilibrium p p 1 p 2 s q hat squareroot s Be able to explain the general pattern of evolution under selection against recessive alleles and contrast it to the pattern under selection against dominance alleles Pattern of evolution under selection against dominant alleles Evolution of the dominant allele will be rapid at first but will slow as the experiment proceeds as shown by the graph p p2w11 pqw12 wbar Frequency of the dominant allele rises wAA wAa 1 s waa 1 Substituting as before p p 1 s 1 2sp sp2 If s 1 then dominant allele is gone in one generation If s is large then p declines rapidly Pattern of evolution under selection against recessive alleles Evolution of the recessive allele will be rapid at first but will slow as the experiment proceeds as shown by the graph Frequency of the recessive allele falls wAA wAa 1 waa 1 s s is the selection coefficient strength of selection against the aa genotype Fitnesses of wAA and wAa are rescaled to one by dividing by wAA Fitness of recessive homozygote rescaled in the same manner Experiment shows that dominance and allele frequency interact to determine the rate of evolution When a recessive allele is common and a dominant allele is rare evolution by natural selection is rapid In contrast when a recessive allele is rare and a dominant allele is common evolution by natural selection is slow It is important to also note that selection may favor or disfavor both kinds of variants as some dominant alleles may be considered deleterious although this is not common Be able to explain …