Population and Evolutionary Genetics

Transcription

1 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page Population and Evolutionary enetics *1. Voles (Microtus ochrogaster) were trapped from old fields in southern Indiana and were genotyped for a transferrin locus. The following numbers of genotypes were recorded. T E T E 407 T E T F 170 T F T F 17 alculate the genotypic and allelic frequencies of the transferrin locus for this population. **2. student tells you that dominant phenotypes should always increase in frequency over recessive phenotypes because mating between two heterozygous individuals produces 3 / 4 offspring with the dominant trait and only 1 / 4 offspring with the recessive trait. Is this student correct? Why or why not? **3. enotypes of Ponderosa pine trees in olorado were determined for a peroxidase locus, and the following data were obtained. (From Mitton et al Journal of Heredity 70: ) enotype Number R 2 R 2 11 R 2 R 3 36 R 3 R 3 4 Total 51 a. alculate the genotypic and allelic frequencies for the peroxidase locus for this population. b. Determine the numbers of the three genotypes expected at Hardy-Weinberg equilibrium. c. Perform a χ 2 test comparing the observed and expected numbers of genotypes. Do you think this population is in Hardy-Weinberg equilibrium? Pierce, enetics: onceptual pproach 69

2 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page 70 Pierce, enetics: onceptual pproach hapter 23 Population and Evolutionary enetics **4. Full color (D) in domestic cats is dominant to dilute color (d). Of 325 cats observed, 194 had full color and 131 had dilute color. a. If these cats are in Hardy-Weinberg equilibrium for the dilution locus, what is the frequency of the dilute allele? b. How many of the 194 cats with full color are heterozygous? *5. The MN blood type in humans is determined by two codominant alleles, L M and L N. The frequency of L M in Eskimos on a small rctic island is If the inbreeding coefficient for this population is 0.05, what are the expected frequencies of the M, MN, and N blood types on the island? **6. In erman cockroaches, curved wing (cv) is recessive to normal wing (cv + ). Bill, who is raising cockroaches in his dorm room, finds that the frequency of the gene for curved wings in his cockroach population is 0.6. In the apartment of his friend Joe, the frequency of the gene for curved wings is 0.2. One day Joe visits Bill in his dorm room, and several cockroaches jump out of Joe s hair and join the population in Bill s room. Bill estimates that 10% of cockroaches in his dorm room now consists of individuals that jumped out of Joe s hair. What will be the new frequency of curved wings among cockroaches in Bill s room? **7. population of water snakes is found on an island in Lake Erie. Some of the snakes are banded and some are unbanded; banding is caused by an autosomal allele that is recessive to an allele for no bands. The frequency of banded snakes on the island is 4%, whereas the frequency of banded snakes on the mainland is 81%. One summer a large number of snakes migrate from the mainland to the island. fter this migration, 20% of the island population consists of snakes that came from the mainland. a. ssuming that both the mainland population and the island population are in Hardy-Weinberg equilibrium for the alleles that affect banding, what are the frequencies of the allele for bands on the island and on the mainland before migration? b. fter migration has occurred, what will be the frequency of the banded allele on the island? **8. Pikas are small mammals that occur at high elevation in the talus slopes of mountains. Populations located on mountaintops in olorado and Montana in North merica are relatively isolated from one another because the pikas don t occupy the low-elevation habitats that separate the mountaintops, and don t venture far from the talus slopes. Thus, there is little gene flow between populations. Furthermore, each population is relatively small in size and was founded by a small number of individuals. group of population geneticists propose using protein electrophoresis to study the amount of genetic variation in a series of pika populations and to compare the allelic frequencies in different populations. Based on the biology and distribution of pikas, what do you predict the population geneticists will find concerning the genetic variation within and between populations? 70

3 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page 71 Pierce, enetics: onceptual pproach hapter 23 Population and Evolutionary enetics **9. Two chromosomal inversions are commonly found in populations of Drosophila psuedoobscura: Standard (ST) and rrowhead (R). When treated with the insecticide DDT, the genotypes for these inversions exhibit overdominance, with the following fitnesses. enotype Fitness ST/ST 0.47 ST/R 1.0 R/R 0.62 What will the frequencies of ST and R be after equilibrium is reached? ***10. The Barton Springs salamander is an endangered species found only in a single spring that occurs within the city of ustin, Texas. There is growing concern that a chemical spill on a nearby freeway could pollute the spring and wipe out the species. To provide a source of salamanders to repopulate the spring in the event of such a catastrophe, a proposal has been made to establish a captive breeding population of the salamander in a local zoo. You are asked to provide a plan for the establishment of this captive breeding population, with the goal of maintaining as much of the genetic variation of the species as possible in the captive population. What factors might cause loss of genetic variation in the establishment of the captive population? How could loss of such variation be avoided? ssuming that it is only feasible to maintain a limited number of salamanders in captivity, what procedures should be instituted to ensure the long-term maintenance of as much of the variation as possible? 71

4 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page 72 Pierce, enetics: onceptual pproach hapter 23 Population and Evolutionary enetics TBLE 1: The enetic ode Second Letter First letter Phe Leu Leu Ile Met Val Ser Pro Thr la Tyr Stop Stop His ln sn Lys sp lu ys Stop Trp rg Ser rg ly Third letter 72

5 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page 73 Pierce, enetics: onceptual pproach hapter 23 Population and Evolutionary enetics TBLE 2: The Wobble Rules The Wobble Rules indicate which bases in the third position (3' end) of the mrn codon can pair with bases at the first (5' end) of the anticodon of the trn. 1st Position 3rd Position nticodon odon Pairing nticodon 3' X Y 5' 5' Y X 3' odon or nticodon 3' X Y 5' 5' Y X 3' odon nticodon 3' X Y 5' 5' Y X 3' odon or nticodon 3' X Y 5' 5' Y X 3' odon I (inosine),, or nticodon 3' X Y I 5' 5' Y X 3' odon 73

6 [ ] PIERE STDENT MN 8/22/01 2:03 PM Page 74 Pierce, enetics: onceptual pproach hapter 23 Population and Evolutionary enetics TBLE 3: ritical Values of the χ 2 Distribution df df