1) Which of the following is the best modern definition of evolution?
A) descent with modification
B) change in the number of genes in a population over time
C) survival of the fittest
D) inheritance of acquired characters
A
2) Which variable is likely to undergo the largest change in value resulting from a mutation that introduces a new allele into a population at a locus for which all individuals formerly had been fully homozygous?
A) average heterozygosity
B) nucleotide variability
C) geographic variability
D) average number of loci
A
3) Which statement about the beak size of finches on the island of Daphne Major during prolonged drought is true?
A) Each bird evolved a deeper, stronger beak as the drought persisted.
B) Each bird's survival was strongly influenced by the depth and strength of its beak as the drought persisted.
C) Each bird that survived the drought produced only offspring with deeper, stronger beaks than seen in the previous generation.
D) The frequency of the strong-beak alleles increased in each bird as the drought persisted.
B
4) Which statement about variation is true?
A) All phenotypic variation is the result of genotypic variation.
B) All genetic variation produces phenotypic variation.
C) All nucleotide variability results in neutral variation.
D) All new alleles are the result of nucleotide variability.
D
5) Rank the following one-base point mutations (from most likely to least likely) with respect to their likelihood of affecting the structure of the corresponding polypeptide.
- insertion mutation deep within an intron
- substitution mutation at the third position of an exonic codon
- substitution mutation at the second position of an exonic codon
- deletion mutation within the first exon of the gene
A) 1, 2, 3, 4
B) 4, 3, 2, 1
C) 2, 1, 4, 3
D) 3, 1, 4, 2
B
6) Genetic variation _____.
A) is created by the direct action of natural selection
B) arises in response to changes in the environment
C) must be present in a population before natural selection can act upon the population
D) tends to be reduced by when diploid organisms produce gametes
C
The questions below refer to the following paragraph.
HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.
7) Which of the following represents the treatment option most likely to avoid the evolution of drug-resistant HIV (assuming no drug interactions or side effects)?
A) using a series of NAs, one at a time, and changed about once a week
B) using a single PI, but slowly increasing the dosage over the course of a week
C) using high doses of NA and a PI at the same time for a period not to exceed one day
D) using moderate doses of NA and two different PIs at the same time for several months
D
8) Every HIV particle contains two RNA molecules. If two genes from one RNA molecule become detached and then, as a unit, get attached to one end of the other RNA molecule within a single HIV particle, which of these is true?
A) There are now fewer genes within the viral particle.
B) There are now more genes within the viral particle.
C) A point substitution mutation has occurred in the retroviral genome.
D) One of the RNA molecules has experienced gene duplication as the result of translocation.
D
The following experiment is used for the corresponding question(s).
A researcher discovered a species of moth that lays its eggs on oak trees. Eggs are laid at two distinct times of the year: early in spring when the oak trees are flowering and in midsummer when flowering is past. Caterpillars from eggs that hatch in spring feed on oak flowers and look like oak flowers. But caterpillars that hatch in summer feed on oak leaves and look like oak twigs.
How does the same population of moths produce such different-looking caterpillars on the same trees? To answer this question, the biologist caught many female moths from the same population and collected their eggs. He put at least one egg from each female into eight identical cups. The eggs hatched, and at least two larvae from each female were maintained in one of the four temperature and light conditions listed below.
In each of the four environments, one of the caterpillars was fed oak flowers, the other oak leaves. Thus, there were a total of eight treatment groups (4 environments × 2 diets).
9) Refer to the accompanying figure. Which one of the following is NOT a plausible hypothesis to explain the differences in caterpillar appearance observed in this population?
A) The longer day lengths of summer trigger the development of twig-like caterpillars.
B) The cooler temperatures of spring trigger the development of flowerlike caterpillars.
C) Differences in air pressure, due to differences in elevation, trigger the development of different types of caterpillars.
D) Differences in diet trigger the development of different types of caterpillars.
C
10) Refer to the accompanying figure. In every case, caterpillars that feed on oak flowers look like oak flowers. In every case, caterpillars that were raised on oak leaves looked like twigs. These results support which of the following hypotheses?
A) The longer day lengths of summer trigger the development of twig-like caterpillars.
B) Differences in air pressure, due to elevation, trigger the development of different types of caterpillars.
C) Differences in diet trigger the development of different types of caterpillars.
D) The differences are genetic. A female will either produce all flowerlike caterpillars or all twig-like caterpillars.
C
11) Refer to the accompanying figure. Recall that eggs from the same female were exposed to each of the eight treatments used. This aspect of the experimental design tested which of the following hypotheses?
A) The longer day lengths of summer trigger the development of twig-like caterpillars.
B) Differences in air pressure, due to elevation, trigger the development of different types of caterpillars.
C) Differences in diet trigger the development of different types of caterpillars.
D) The differences are genetic. A female will either produce all flowerlike caterpillars or all twig-like caterpillars.
D
12) Cystic fibrosis is a genetic disorder in homozygous recessives that causes death during the teenage years. If 9 in 10,000 newborn babies have the disease, what are the expected frequencies of the dominant (A1) and recessive (A2) alleles according to the Hardy-Weinberg model?
A) f(A1) = 0.9997, f(A2) = 0.0003
B) f(A1) = 0.9800, f(A2) = 0.0200
C) f(A1) = 0.9700, f(A2) = 0.0300
D) f(A1) = 0.9604, f(A2) = 0.0392
C
13) Suppose 64% of a remote mountain village can taste phenylthiocarbamide (PTC) and must, therefore, have at least one copy of the dominant PTC taster allele. If this population conforms to Hardy-Weinberg expectations for this gene, what percentage of the population must be heterozygous for this trait?
A) 16%
B) 32%
C) 40%
D) 48%
D
14) For biologists studying a large flatworm population in the lab, which Hardy-Weinberg condition is most difficult to meet?
A) no selection
B) no genetic drift
C) no gene flow
D) no mutation
D
15) For a biologist studying a small fish population in the lab, which Hardy-Weinberg condition is easiest to meet?
A) no selection
B) no genetic drift
C) no gene flow
D) no mutation
C
Use the following information to answer the question(s) below.
Researchers studying a small milkweed population note that some plants produce a toxin and other plants do not. They identify the gene responsible for toxin production. The dominant allele (T) codes for an enzyme that makes the toxin, and the recessive allele (t) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The genotypes of all individuals in the population are determined (see chart) and used to determine the actual allele frequencies in the population.
16) Refer to the figure above. Is this population in Hardy-Weinberg equilibrium?
A) Yes.
B) No; there are more heterozygotes than expected.
C) No; there are more homozygotes than expected.
D) More information is needed to answer this question.
C
17) If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be _____.
A) 23%
B) 46%
C) 54%
D) 92%
C
18) The higher the proportion of loci that are "fixed" in a population, the lower are that population's _____.
A) nucleotide variability
B) chromosome number
C) average heterozygosity
D) nucleotide variability and average heterozygosity
D
19) Whenever diploid populations are in Hardy-Weinberg equilibrium at a particular locus, _____.
A) the allele's frequency should not change from one generation to the next
B) natural selection, gene flow, and genetic drift are acting equally to change an allele's frequency
C) two alleles are present in equal proportions
D) individuals within the population are evolving
A
20) In the formula for determining a population's genotype frequencies, the "2" in the term 2pq is necessary because _____.
A) the population is diploid
B) heterozygotes can come about in two ways
C) the population is doubling in number
D) heterozygotes have two alleles
B
21) In the formula for determining a population’s genotype frequencies, the "pq" in the term 2pq is necessary because _____.
A) the population is diploid
B) heterozygotes can come about in two ways
C) the population is doubling in number
D) heterozygotes have two alleles
D
22) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of the allele a is 0.3. What is the frequency of individuals that are homozygous for this allele?
A) 0.09
B) 0.49
C) 0.9
D) 9.0
A
23) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.2. What is the frequency of individuals that are heterozygous for this allele?
A) 0.020
B) 0.04
C) 0.16
D) 0.32
D
24) In a Hardy-Weinberg population with two alleles, A and a, that are in equilibrium, the frequency of allele a is 0.1. What is the frequency of individuals with AA genotype?
A) 0.20
B) 0.32
C) 0.42
D) 0.81
D
25) You sample a population of butterflies and find that 56% are heterozygous at a particular locus. What should be the frequency of the recessive allele in this population?
A) 0.08
B) 0.09
C) 0.70
D) Allele frequency cannot be determined from this information.
D
26) In peas, a gene controls flower color such that R = purple and r = white. In an isolated pea patch, there are 36 purple-flowering plants and 64 white-flowering plants. Assuming Hardy-Weinberg equilibrium, what is the value of q for this population?
A) 0.36
B) 0.64
C) 0.75
D) 0.80
D
Use the following information to answer the question(s) below.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.
27) What is the most reasonable conclusion that can be drawn from the fact that the frequency of the recessive trait (aa) has not changed over time?
A) The two phenotypes are about equally adaptive under laboratory conditions.
B) The genotype AA is lethal.
C) There has been a high rate of mutation of allele A to allele a.
D) There has been sexual selection favoring allele a.
A
Use the following information to answer the question(s) below.
A large population of laboratory animals has been allowed to breed randomly for a number of generations. After several generations, 25% of the animals display a recessive trait (aa), the same percentage as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants.
28) What is the estimated frequency of allele A in the gene pool?
A) 0.25
B) 0.50
C) 0.75
D) 0.125
B
29) What proportion of the population is probably heterozygous (Aa) for this trait?
A) 0.05
B) 0.25
C) 0.50
D) 0.75
C
30) Mutation is the only evolutionary mechanism that _____.
A) does little to change allele frequencies
B) is more important in eukaryotes than in prokaryotes
C) happens in all populations
D) has no effect on genetic variation
A
The following question(s) are based on information in Hopi E. Hoekstra, Kristen E. Drumm, and Michael W. Nachman, "Ecological Genetics of Adaptive Color Polymorphism in Pocket Mice: Geographic Variation in Selected and Neutral Genes," Evolution 58(6), 2004: 1329-41.
31) The figure above shows the distribution of pocket-mouse coat colors in several Arizona populations found either on light-colored granite substrate or on dark volcanic rock (dark substrate). The Melanocortin-1 receptor (Mc1r) alleles, D and d, differ by four amino acids. Mice with DD and Dd genotypes have dark coats, whereas mice with the dd genotype are light colored. What sort of genotype frequencies might you expect to find in the Xmas, Mid, and O'Neill populations?
A) Xmas-high DD frequency; Mid-high Dd frequency, O'Neill-high dd frequency
B) Xmas-high Dd frequency; Mid-high DD frequency, O'Neill-high dd frequency
C) Xmas-high dd frequency; Mid-high Dd frequency, O'Neill-high DD frequency
D) Xmas-high dd frequency; Mid-high DD frequency, O'Neill-high Dd frequency
D
32) Refer to the figure above. In their investigation of natural selection on Mc1r alleles (the gene that determines coat color) in Arizona pocket mice, Hoekstra et al. determined the frequency of the D and d alleles in each population. They also determined the frequency of alleles for two neutral mitochondrial DNA genes (genes that do not affect and are not linked to coat color). Why did the researchers include the mitochondrial DNA genes as part of their experimental design?
A) Allele change for the neutral mitochondrial genes serves as an experimental group and gives information on any general background genetic difference among these populations.
B) Allele change for the neutral mitochondrial genes serves as a control and determines coat-color differences among these populations.
C) Allele change for the neutral mitochondrial genes serves as an experimental group and gives information on coat-color differences among these populations.
D) Allele change for the neutral mitochondrial genes serves as a control and gives information on any general background genetic difference among these populations.
D
33) Soon after the island of Hawaii rose above the sea surface (somewhat less than one million years ago), the evolution of life on this new island should have been most strongly influenced by _____.
A) a genetic bottleneck
B) sexual selection
C) habitat differentiation
D) the founder effect
D
Use the following information to answer the question(s) below.
In 1983 a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.)
34) Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails were, on average, 36% white, whereas the tails of males from nearby mountain populations averaged 40-45% white. If this observed trait difference were due to a difference in the original colonizing population, it would most likely be due to _____.
A) mutations in the UCSD population
B) gene flow between populations
C) a genetic bottleneck
D) a founder effect
D
In 1983 a population of dark-eyed junco birds became established on the campus of the University of California, San Diego (UCSD), which is located many miles from the junco's normal habitat in the mixed-coniferous temperate forests in the mountains. Juncos have white outer tail feathers that the males display during aggressive interactions and during courtship displays. Males with more white in their tail are more likely to win aggressive interactions, and females prefer to mate with males with more white in their tails. Females have less white in their tails than do males, and display it less often. (Pamela J. Yeh. 2004. Rapid evolution of a sexually selected trait following population establishment in a novel habitat. Evolution 58[1]:166-74.)
35) Refer to the paragraph on dark-eyed junco birds. The UCSD campus male junco population tails are about 36% white, whereas the tails of males from nearby mountain populations are about 40-45% white. The founding stock of UCSD birds was likely from the nearby mountain populations because some of those birds overwinter on the UCSD campus each year. Population sizes on the UCSD campus have been reasonably large, and there are significant habitat differences between the UCSD campus and the mountain coniferous forests; UCSD campus has a more open environment (making birds more visible) and a lower junco density (decreasing intraspecific competition) than that in the mountain forests. Given this information, which of the following evolutionary mechanisms do you think is most likely responsible for the difference between the UCSD and mountain populations?
A) natural selection
B) genetic drift
C) gene flow
D) mutation
A
36) The Dunkers are a religious group that moved from Germany to Pennsylvania in the mid-1700s. They do not marry with members outside their own immediate community. Today, the Dunkers are genetically unique and differ in gene frequencies, at many loci, from all other populations including those in their original homeland. Which of the following likely explains the genetic uniqueness of this population?
A) population bottleneck and Hardy-Weinberg equilibrium
B) heterozygote advantage and stabilizing selection
C) mutation and natural selection
D) founder effect and genetic drift
D
37) An earthquake decimates a ground-squirrel population, killing 98% of the squirrels. The surviving population happens to have broader stripes, on average, than the initial population. If broadness of stripes is genetically determined, what effect has the ground-squirrel population experienced during the earthquake?
A) directional selection
B) disruptive selection
C) a founder event
D) a genetic bottleneck
D
38) Which of the following is the most predictable outcome of increased gene flow between two populations?
A) lower average fitness in both populations
B) higher average fitness in both populations
C) increased genetic difference between the two populations
D) decreased genetic difference between the two populations
D
39) In 1986, a nuclear power accident in Chernobyl, USSR (now Ukraine), led to high radiation levels for miles surrounding the plant. The high levels of radiation caused elevated mutation rates in the surviving organisms, and evolutionary biologists have been studying rodent populations in the Chernobyl area ever since. Based on your understanding of evolutionary mechanisms, which of the following most likely occurred in the rodent populations following the accident?
A) Mutations caused major changes in rodent physiology over time.
B) Mutation led to increased genetic variation.
C) Mutation caused genetic drift and decreased fitness.
D) Mutation caused the fixation of new alleles.
B
40) Over time, the movement of people on Earth has steadily increased. This has altered the course of human evolution by increasing _____.
A) nonrandom mating
B) geographic isolation
C) genetic drift
D) gene flow
D
41) You are maintaining a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, you notice that the viability of the flies has decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, the best way to reverse this trend is to _____.
A) cross your flies with flies from another lab
B) reduce the number of flies that you transfer at each generation
C) transfer only the largest flies
D) change the temperature at which you rear the flies
A
42) The inability of organisms to evolve anything that could be an advantage reflects _____.
A) the limits of historical constraints
B) the inability to compromise
C) the consequences of random mutations
D) the consequences of inbreeding
A
43) Which of the following is a fitness trade-off (compromise)?
A) In some hornbill species, the male helps seal the female in a tree with her nest until the young are ready to fledge.
B) Hummingbirds are the best pollinators of certain flowers, but bees are the best pollinators for orchids.
C) The strong, thick beak of a woodpecker helps it find insects in trees.
D) Turtle shells provide protection but are heavy and burdensome when moving.
D
Use the following description to answer the question(s) below.
On the Bahamian island of Andros, mosquitofish populations live in various, now-isolated, freshwater ponds that were once united. Currently, some predator-rich ponds have mosquitofish that can swim in short, fast bursts; other predator-poor ponds have mosquitofish that can swim continuously for a long time. When placed together in the same body of water, the two kinds of female mosquitofish exhibit exclusive breeding preferences.
44) If one builds a canal linking a predator-rich pond to a predator-poor pond, then what type(s) of selection should subsequently be most expected among the mosquitofish in the original predator-rich pond, and what type(s) should be most expected among the mosquitofish in the formerly predator-poor pond?
A) stabilizing selection; directional selection
B) stabilizing selection; stabilizing selection
C) less-intense directional selection; more-intense directional selection
D) less-intense disruptive selection; more-intense disruptive selection
C
Use the following information to answer the question(s) below.
Martin Wikelski and L. Michael Romero (Body size, performance and fitness in Galápagos marine iguanas, Integrative and Comparative Biology 43 [2003]:376-86) measured the snout-to-vent (anus) length of Galápagos marine iguanas and observed the percent survival of different-sized animals, all of the same age. The graph shows the log snout-vent length (SVL, a measure of overall body size) plotted against the percent survival of these different size classes for males and females.
45) Examine the figure above. What type of selection for body size appears to be occurring in these marine iguanas?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) You cannot determine the type of selection from the above information.
B
46) Currently the only predators of Galápagos marine iguanas are Galápagos hawks. Iguana body size is not correlated with risk of hawk predation, although small iguanas can sprint faster than large iguanas. If predators (for example, cats) that preferably catch and eat slower iguanas are introduced to the island, iguana body size is likely to _____ in the absence of other factors; the iguanas would then be under _____ selection.
A) increase; directional
B) increase; disruptive
C) decrease; directional
D) decrease; disruptive
C
47) Three-spined stickleback fish (Gasterosteus aculeatus) show substantial heritable variation in gill-raker length related to differences in their diets. Longer gill rakers appear to function better for capturing open-water prey, while shorter gill rakers function better for capturing shallow-water prey. Which of the following types of selection is most likely to be found in a large lake (open water in the middle and shallow water around the sides) with a high density of these fish?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) sexual selection
C
48) A biologist doing a long-term study on a wild spider population observes increased variation in silk thickness. Which of the following could the spider population be experiencing?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) genetic drift
C
49) In some jacana species, males take care of the eggs and young, and females compete among themselves for territories that contain one to several males. Female jacanas are significantly larger than males. Which of these statements would you predict to be true of this bird species?
- Male jacana fitness is primarily limited by ability to take care of eggs and raise young.
- Female jacana fitness is limited by the number of males in her territory with which a female mates.
- Variation in reproductive success should be greater in male jacanas than in females.
- Variation in reproductive success should be greater in female jacanas than in males.
- Males and females have equal variation in reproductive success.
A) 1 and 3
B) 2 and 4
C) 1, 2, and 4
D) 5
C
50) The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. The outcome of the conflict between bacteria and bacteriophage at any point in time results from _____.
A) frequency-dependent selection
B) evolutionary imbalance
C) heterozygote advantage
D) neutral variation
A
51) The restriction enzymes of bacteria protect the bacteria from successful attack by bacteriophages, whose genomes can be degraded by the restriction enzymes. The bacterial genomes are not vulnerable to these restriction enzymes because bacterial DNA is methylated. This situation selects for bacteriophages whose genomes are also methylated. As new strains of resistant bacteriophages become more prevalent, this in turn selects for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Over the course of evolutionary time, what should occur?
A) Methylated DNA should become fixed in the gene pools of bacterial species.
B) Nonmethylated DNA should become fixed in the gene pools of bacteriophages.
C) Methylated DNA should become fixed in the gene pools of bacteriophages.
D) Methylated and nonmethylated strains should be maintained among both bacteria and bacteriophages, with ratios that vary over time.
D
52) Arrange the following in order from most general to most specific.
- natural selection
- microevolution
- intrasexual selection
- evolution
- sexual selection
A) 4, 1, 2, 3, 5
B) 4, 2, 1, 3, 5
C) 4, 2, 1, 5, 3
D) 1, 4, 2, 5, 3
C
53) Adult male humans generally have deeper voices than do adult female humans, which is the direct result of higher levels of testosterone causing growth of the larynx. If the fossil records of apes and humans alike show a trend toward decreasing larynx size in adult females and increasing larynx size in adult males, then _____.
A) sexual dimorphism was evolving over time in these species
B) intrasexual selection seems to have occurred in both species
C) stabilizing selection was occurring in these species concerning larynx size
D) selection was acting more directly upon genotype than upon phenotype
A
54) Most Swiss starlings produce four to five eggs in each clutch. Starlings producing fewer or more than this have reduced fitness. Which of the following terms best describes this situation?
A) directional selection
B) stabilizing selection
C) disruptive selection
D) sexual selection
B
55) When imbalances occur in the sex ratio of sexual species that have two sexes (that is, other than a 50:50 ratio), the members of the minority sex often receive a greater proportion of care and resources from parents than do the offspring of the majority sex. This is most clearly an example of _____.
A) sexual selection
B) balancing selection
C) stabilizing selection
D) frequency-dependent selection
D
56) A proficient engineer can easily design skeletal structures that are more functional than those currently found in the forelimbs of such diverse mammals as horses, whales, and bats. The actual forelimbs of these mammals do not seem to be optimally arranged because _____.
A) natural selection has not had sufficient time to create the optimal design in each case, but will do so given enough time
B) in many cases, phenotype is determined by genotype and the environment
C) though we may not consider the fit between the current skeletal arrangements and their functions excellent, we should not doubt that natural selection ultimately produces the best design
D) natural selection is generally limited to modifying structures that were present in previous generations and in previous species
D
In a very large population, a quantitative trait has the following distribution pattern.
58) If there is no gene flow, the curve shifts to the left or to the right, and the population size consequently increases over successive generations, which of the following is most likely occurring?
A) immigration or emigration
B) directional selection
C) disruptive selection
D) genetic drift
B
Use the following information to answer the question(s) below.
In those parts of equatorial Africa where the malaria parasite is most common, the sickle-cell allele constitutes 20% of the β hemoglobin alleles in the human gene pool.
59) In the United States, the parasite that causes malaria is not present, but African-Americans whose ancestors were from equatorial Africa are present. What should be happening to the sickle-cell allele in the United States, and what should be happening to it in equatorial Africa?
A) stabilizing selection; disruptive selection
B) disruptive selection; stabilizing selection
C) directional selection; disruptive selection
D) directional selection; stabilizing selection
D
60) Swine are vulnerable to infection by bird flu virus and human flu virus, which can both be present in an individual pig at the same time. When this occurs, it is possible for genes from bird flu virus and human flu virus to be combined. If the human flu virus contributes a gene for Tamiflu resistance (Tamiflu is an antiviral drug) to the new virus, and if the new virus is introduced to an environment lacking Tamiflu, then what is most likely to occur?
A) The new virus will maintain its Tamiflu-resistance gene, in case of future exposure to Tamiflu.
B) The Tamiflu-resistance gene will undergo mutations that convert it into a gene that has a useful function in this environment.
C) If the Tamiflu-resistance gene involves a cost, it will experience directional selection leading to reduction in its frequency.
D) If the Tamiflu-resistance gene confers no benefit in the current environment, and has no cost, the virus will increase in frequency.
C