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Name: ____________________________________ Genetics 314 – Spring, 2004 Exam 5 – 100 points 1. You have become intrigued with aquaculture, the ‘farming’ of fish for food. You decide to become a fish breeder and breed designer trout for restaurants. You discover most of the traits you are interested in are under quantitative control and have a heritability (h2) of less than .4. a) What is meant when a trait is under quantitative control? If a trait is under quantitative genetic control then it is a trait that is controlled by several to many genes with each gene having only a minor effect on expression of the trait. Because of the number of genes there are usually no distinct phenotypes with a quantitative trait, instead you have more of a gradient of expression from one extreme to the other. b) How much success will you have in breeding for improved trout with the given heritability? Briefly explain your answer. It is possible to make some improvement in the trait but the amount of the trait under genetic control is relatively low with a h2 of less than .4. This means that less than 40% of the variation observed for the trait is under genetic control. 2. You decide to breed for rapid growth in a trout population. You have a population with an average weight gain of 50 grams/month. You want to improve that to 75 grams/month so you select a population for breeding that has an average weight gain of 90 grams/month. a) If you have a heritability (h2) of .33 what would be the increase in average weight gain/month after one generation? genetic gain = h2(mean sel pop – mean org pop) = .33(90 – 50) = .33 x 40 = 13.2 grams per month or the new population mean would be 63.5 grams per month b) Did you attain your goal? If not what could you have done differently to achieve your target average weight gain per month? No, the goal was 75 grams per month and the new population mean will only be 63.5 grams per month. If possible select a population with a higher mean average weight gain per month (greater than 90 grams per month). 1 Name: ____________________________________ You have decided fish farming is not for you but you want to stay in fish genetics. You observe that there are several colors of trout possible from iridescent blue to a color best described as ‘stealth’ because it makes the fish impossible to spot from the surface. You find a population that these two colors are the primary colors of the fish and that the two colors, iridescent blue (IB) and stealth (ib), are due to allelic variations at the same gene locus with iridescent blue being the dominant allele. The following questions will relate to this population. 3. You discover this population in an underground river and realize that the population has been under no selection pressure due to its location and that it could be an example of a population that meets the criteria for being in Hardy-Weinberg equilibrium. You collect the following data on the fish population: iridescent blue (IB_) 840 stealth (ibib) 160 a) What is meant when a population is said to be in Hardy-Weinberg equilibrium? If a population is in Hardy-Weinberg equilibrium then the allelic and genotypic frequencies should remain constant over generations. It also means that there are no evolutionary forces at work, there is an unlimited population size, no mating preference (random mating) and no differences in gamete or progeny viability. b) If the population is in Hardy-Weinberg equilibrium, please calculate the allelic and genotypic frequencies for your population. q2 = 160/1000 = .160 so q would equal the square root of q2 (.16) or .4 If q = .4 then p = (1 – q) = (1 - .4) = .6 So the allelic frequencies are IB = .6 and ib = .4 For genotypic frequencies use the formula p2 + 2pq + q2 IBIB = p2 = .62 = .36 IBib = 2pq = 2 x .6 x .4 = 2 x .24 = .48 ibib = q2 = .42 = .16 4. In studying your color trait you discover the difference between iridescent blue and stealth is a single base change mutation. Working with a sub-population with allelic frequencies of IB = .7 and ib = .3 you determine that the forward mutation rate (IB to ib) is 7 x 10-5 and the back mutation rate (ib to IB) is 5 x 10-6. a) What is the change in the allelic frequency of ib after one generation? ∆q = up – vq = (7 x 10-5 x .7) – (5 x 10-6 x .3) = 4.9 x 10-5 – 1.5 x 10-6 = 4.75 x 10-5 2 Name: ____________________________________ b) If mutation was the only evolutionary force at work, what would the equilibrium frequency of ib be? qequil = u / (u + v) = 7 x 10-5 / (7 x 10-5 + 5 x 10-6) = 7 x 10-5 / 7.5 x 10-5 = 7 / 7.5 = 0.933 So the equilibrium frequency for ib would be .933 if mutation was the only evolutionary force acting on the population. 5. You are curious if the iridescent blue color gives a selective advantage to the trout in the underground river. You develop molecular markers to differentiate each genotype and tag an equal number of individuals and follow their survival and reproduction for one generation. You collect the following data: genotype initial pop. IBIB IBib ibib 500 500 500 surviving pop. total progeny 300 250 400 30,000 10,000 8,000 a) What are the absolute fitness values for each genotype? genotype IBIB IBib ibib surviving pop. ave. no. progeny absolute fitness 300/500 = .6 250/500 = .5 400/500 = .8 30,000/300 = 100 10,000/250 = 40 8,000/400 = 20 .6 x 100 = 60 .5 x 40 = 20 .8 x 20 = 16 b) What are the relative fitness values for each genotype? genotype IBIB IBib ibib absolute fitness/ optimum absolute fitness = relative fitness 60 / 60 = 1 20 / 60 = .33 16 / 60 = .27 c) What are the selection coefficients for each genotype? genotype IBIB IBib ibib 1 – relative fitness = selection coefficient 1–1=0 1 - .33 = .67 1 - .27 = .73 3 Name: ____________________________________ d) How will the genotypic and/or allelic frequencies change due to selection? The number of homozygous dominant (IBIB) or blue individuals will increase while the number of heterozygous and homozygous recessive (ibib) individuals will decrease. This will result in the allelic frequency of IB increasing and the allelic frequency of ib decreasing. 6. What are the three types of selection and how do they differ? The three types of selection are directional, stabilizing and destabilizing and they differ by which genotype is being favored. In directional selection one of the homozygous genotypes is being selected. In stabilizing the heterozygous genotype is being favored over the two homozygous genotypes. In destabilizing both homozygous genotypes are favored and the heterozygous genotype is being selected against. 7. During exploratory drilling for natural gas in an adjoining wilderness area an above ground river is accidentally connected with the underground river and trout from the above ground river migrate into your population before the error is discovered. If your population of 3000 fish had allelic frequencies of IB = .8 and ib = .2 and 600 above ground fish with allelic frequencies of IB = .9 and ib = .1 migrated into the underground river; a) What is the change in allelic frequencies in your population due to migration? ∆p = m(pmig – porg) migration rate (m) = no. of migrants / total population (no. original pop + migrants) m = 600 / (3000 + 600) = 600 / 3600 = .1667 ∆p = .1667(.9 - .8) = .1667 x .1 = .01667 p = p + ∆p = .8 + .01667 = .81667 q = 1 – p = 1 - .81667 = .1833 b) What two factors control the level of impact of migration? The two factors that control the level of impact of migration on the allelic frequencies of a population are the migration rate and the difference in the allelic frequencies of the two populations. 4 Name: ____________________________________ 8. A mining enterprise in the wilderness area discovers the underground river upstream from your population and diverts the water for placer mining. Alarmed by the sudden drop in water you rush to save as many fish as possible to preserve the population but you only have enough buckets to save 100 fish. You have three possible subpopulations you can save: population 1 2 3 no. males 30 40 45 no. females IB ib 70 60 55 .7 .6 .9 .3 .4 .1 a) What is the effective population size of each sub-population? Use the following formulat to calculate effective population size Ne = (4 x Nm x Nf)/(Nm + Nf) pop 1 = (4 x 30 x 70) / (30 + 70) = 8,400/100 = 84 pop 2 = (4 x 40 x 60) / (40 + 60) = 9,600/100 = 96 pop 3 = (4 x 45 x 55) / (45 + 55) = 9,900/100 = 99 b) If you wanted to preserve genetic variability in your population which subpopulation would you want to save and why? To preserve genetic variability you would want the largest population with the smallest difference in allelic frequencies. Population 2 would be the best population with an effective population size of 96 and an allelic difference of .2. Population 3 has a slightly larger effective population size but it has the largest difference in allelic frequencies (.8) of the 3 populations. 9. You are concerned about inbreeding having a detrimental effect on your new population. a) What is the potential problem with inbreeding? Inbreeding allows for the expression of deleterious recessive alleles causing a reduction in the fitness of a population. This can also lead to a loss of genetic variability as alleles in the population become fixed or are lost. b) What factors affect the impact inbreeding will have on allelic frequencies in a population? Key factors affecting the impact of inbreeding are effective population size, ratio of males to females and allelic frequencies on the population. 5 Name: ____________________________________ 10. The IB allele appears favorable in underground situations but could be considered a genetic load on the population in above ground rivers. What is meant by genetic load and is it necessarily bad for the trout population? A genetic load indicates that a specific allele or genotype causes a reduction in the overall fitness of a population because it is not considered the optimum genotype for the population. This does reduce the fitness of the population but it also maintains genetic diversity in the population allowing the population to change if the environment (selection pressure) changes. 11. What three things would need to occur for your iridescent blue trout to become a new species? Briefly explain your answer. 1. Something needs to cause a change in allelic frequencies such as mutation, selection or genetic drift. 2. Sub-populations must be geographically isolated so they are in different environments (different selection pressures) and can not inter-mate. 3. Enough time must be allowed to occur to allow any allelic changes to become fixed in the different sub-populations. 6