BIOL 3306 Evolutionary Biology

Transcription

1 BIOL 3306 Evolutionary Biology Maximum score: 22.5 Time Allowed: 90 min Total Problems: The figure below shows two different hypotheses for the phylogenetic relationships among several major groups of animals. X and Y represent ancestral species. Branch lengths do not reflect time precisely. Which of the following statements is correct? a) In tree B, Y is the most recent common ancestor of Arthropoda and Mollusca. b) In tree B, Y is the most recent common ancestor of Annelida and Nematoda. c) In tree B, Y is the most recent common ancestor of Arthropoda and Echinodermata. d) In tree A, X is the most recent common ancestor of Nematoda and Cnidaria. e) In tree A, X is the most recent common ancestor of Echinodermata and Chordata. 2. Which of the following statements is representative of the theory of evolution? a) Natural selection is not a mechanism of evolution. b) Life on earth evolved from one primitive species that lived more than 3.5 billion years ago. c) Life on earth evolved suddenly, over a few generations. d) Natural selection is the only mechanism of evolution. e) Life on earth evolved from many primitive species that lived approximately 350 million years ago. 3. Which of the following conditions is necessary for the operation of natural selection within a population? a) Variation among individuals has no effect on their ability to survive or reproduce. b) Allele frequencies do not change from one generation to the next. c) There is no variation among individuals in the population. d) Individuals in the population are not identical. e) None of the variation among individuals is heritable.! 1!

2 4. Which of the following statements about mutation is correct? a) Transitions are often more common than transversions. b) The mutation rate per base pair per replication is relatively constant among DNA based microorganisms. c) Mutations are largely directed. d) Most mutations with detectable effects on fitness are neutral. e) Beneficial mutations are more common than deleterious mutations 5. Olfactory receptors constitute a large gene family in the vertebrates. Approximately 1000 olfactory receptor genes have been identified in humans, but 60% of these genes have incomplete sequences or show one or more frame disruptions, such as frameshifts or in-frame stop codons. What predictions would you make based on these data? a) A species of mammal with less well developed olfaction than humans should have more than 40% functional olfactory receptor genes. b) Humans should contain a larger proportion of functional olfactory receptor genes than chimpanzees. c) A species of mammal with less well developed olfaction than humans should have less than 40% functional olfactory receptor genes. d) Humans should contain a larger proportion of olfactory receptor pseudogenes than chimpanzees. e) A species of mammal with better developed olfaction than humans should have less than 40% functional olfactory receptor genes. 6. Which of the following statements best describes the process of neofunctionalization? a) A functional gene duplicates. One of the gene copies acquires mutations that make it lose the function of the ancestral gene, but allow it to perform a new function. The other gene copy keeps performing the function of the ancestral gene. b) A pseudogene duplicates. One of the gene copies acquires mutations that make it lose the function of the ancestral gene. The other gene copy acquires mutations that make it lose the function of the ancestral gene. c) A functional gene duplicates. One of the gene copies acquires mutations that make it lose the function of the ancestral gene. The other gene copy keeps performing the function of the ancestral gene. d) A functional gene duplicates. One of the gene copies acquires mutations that make it lose the function of the ancestral gene. The other gene copy acquires mutations that make it lose the function of the ancestral gene. e) A pseudogene duplicates. One of the gene copies acquires mutations that make it lose the function of the ancestral gene, but allow it to perform a new function. The other gene copy keeps performing the function of the ancestral gene.! 2!

3 7. Which of the following evolutionary mechanisms can lead a population to show fewer heterozygotes than expected under Hardy-Weinberg equilibrium? a) Dominance. b) Nonrandom mating. c) Infinite population size. d) Recombination. e) One allele is rare. 8. Natural selection is to Evolutionary change as... a) Plate tectonics is to Continental drift. b) Directed mutation is to the Inheritance of acquired characters. c) Undirected mutation is to Directed mutation. d) Continental drift is to Plate tectonics. e) Pattern is to Mechanism. 9. In humans, the CCR5 locus codes for a cell surface protein found on white blood cells which acts as a fusion coreceptor for HIV-1. The normal allele at this locus is denoted +. An allele containing a 32-base pair deletion in the coding region,!32, is associated with increased resistance to HIV-1 infection. A survey found the following relative genotypic frequencies: +/+ : /!32 : !32/!32 : Calculate the frequency of the + allele? a) 0.36 b) 0.51 c) 0.74 d) 0.63 e) Which of the following evolutionary mechanisms involving natural selection can give rise to the stable, long-term coexistence of two or more alleles at the same locus. a) Inbreeding. b) Selection for beneficial mutations. c) Heterozygote disadvantage. d) Hardy-Weinberg equilibrium. e) Heterozygote advantage.! 3!

4 11. Natural selection may favor non-poisonous butterflies that have the same color pattern as poisonous butterflies, a phenomenon called Batesian mimicry. When the non-poisonous mimics are rare, birds tend to avoid them because they have already encountered poisonous butterflies of the same appearance. But when the non-poisonous mimics are common, the previous encounters of birds with butterflies of their appearance are more likely to have been rewarding; therefore the birds will not avoid eating the non-poisonous butterflies, and the fitness of the mimics will be lower. Populations of the non-poisonous swallowtail butterfly Papilio memnon fit the evolutionary scenario described above. Two alleles (+ and P) at the P locus control color pattern. P/P individuals have the same color pattern as a poisonous species of Papilio, whereas +/+ and P/+ individuals do not. Which of the following plots shows a plausible relationship between fitness of P/P and frequency of the P allele? a) B b) All c) A d) C e) B and D! 4!

5 12. A population of the land snail Cepaea nemoralis shows variation in the intensity of its shell pigmentation determined by one locus with two alleles, D and d: DD individuals have dark shells, whereas dd individuals have light shells. All Dd individuals die during their larval stage and never reach adulthood. Dark shells absorb solar energy more efficiently than light shells, so that individuals with dark shells have a fitness 20% lower than those with light shells. Which of the following plots shows a plausible relationship between mean fitness of the population and frequency of the D allele? a) B b) None c) A d) D e) C 13. Which statement best summarizes the following equation? a) Allele frequencies change as if to increase the mean fitness of the population. b) Allele frequencies change as if to increase the fitness of the different genotypes. c) Mean fitness changes as if to stabilize changes in allele frequency. d) Allele frequencies change as if to stabilize the mean fitness of the population. e) Allele frequencies change as if to lower the mean fitness of the population.! 5!

6 14. A large population of the ciliate Tetrahymena vorax is fixed for the A 1 allele at the A locus. Two beneficial alleles, A 2 and A 3, appear in this population by mutation. The following fitness relationships are observed, where w ij is the fitness of the A i A j genotype: w 11 = w 12 < w 22 w 11 < w 13 = w 33 w 22 = w 23 = w 33 Which allele, A 2 or A 3, would you expect to reach fixation first? a) A 3 because it is recessive. b) A 3 because it is dominant. c) Neither: both alleles will be maintained indefinitely in a stable equilibrium, because there is heterozygote advantage. d) A 2 because it is recessive. e) A 2 because it is dominant. 15. A population of the Eastern Canary Island Lizard (Gallotia atlantica) is composed of two subpopulations, 1 and 2. A large number of individuals were sampled from each subpopulation and genotyped for a locus A. Two alleles were found in both populations: A and a. The frequencies of A in each population are p 1 = 0.6 and p 2 = 0.8, respectively. Both populations were found to be in Hardy-Weinberg (HW) equilibrium. What is the frequency of Aa individuals in the global population constituted by the two subpopulations? a) 0.42 b) 0.61 c) 0.85 d) 0.4 e) 0.63! 6!

7 16. In a population of Drosophila virilis there is a single nucleotide polymorphism locus in the vicinity of the ato (atonal) gene with two alleles: G and C. A population genetic study found the following absolute genotypic frequencies: - G / G : G / C : 97 - C / C : 30 (total 251 individuals). Test whether the population is in Hardy-Weinberg equilibrium at this locus? a) Chi-squared statistic = 1.6. The population does not show a significant deviation from Hardy- Weinberg equilibrium. b) Chi-squared statistic = The population shows a significant deviation from Hardy- Weinberg equilibrium. c) Chi-squared statistic = The population does not show a significant deviation from Hardy-Weinberg equilibrium. d) Chi-squared statistic = The population shows a significant deviation from Hardy- Weinberg equilibrium. e) Chi-squared statistic = 1.6. The population shows a significant deviation from Hardy- Weinberg equilibrium.! 7!

8 17. What does the expression imperfect adaptation mean? Give two real examples of imperfect adaptation. Explain how evolution can lead to imperfect adaptation.!! 8!