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Exam 23: Microevolution

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Question 21

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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 (A2A2) , the same percent as at the beginning of the breeding program. The rest of the animals show the dominant phenotype, with heterozygotes indistinguishable from the homozygous dominants. What proportion of the population is most likely heterozygous (A1A2) for this trait?

A) 0.05
B) 0.25
C) 0.50
D) 0.75

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Question 22

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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. One allele (T1) codes for an enzyme that makes the toxin, and another allele (T2) codes for a nonfunctional enzyme that cannot produce the toxin. Heterozygotes produce an intermediate amount of toxin. The researchers measured the abundance of each of the three possible genotypes and compared those numbers to the expected numbers if the population were in Hardy-Weinberg equilibrium. Those numbers are shown in the chart. Based on these data, which answer correctly identifies whether the population is likely in Hardy-Weinberg equilibrium?

A) Yes, the population appears to be in Hardy-Weinberg equilibrium.
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.

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Question 23

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A population of dark-eyed junco birds became established near the California coastline, 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. Population sizes in the coastal areas have been reasonably large, and there are significant differences between the coastal and the mountain habitats. The coastal habitat is more open (making birds more visible) and has a lower junco density (decreasing intraspecific competition) than the mountain forests. Given this information, which of the following evolutionary mechanisms is the most likely cause of the difference between the coastal and mountain populations?

Which of the following statements is accurate with regard to a population in Hardy-Weinberg equilibrium?

Imagine a small herbaceous flowering plant whose conservation status is "endangered." Which of the following possible experiments would best test if a lack of genetic variability was partially responsible for low population numbers?

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

Which one of the following conditions would most likely cause allele frequencies to change by chance?

In a Hardy-Weinberg population with two alleles A1 and A2 that are in equilibrium, the frequency of allele A2 is 0.2. What is the frequency of individuals that are heterozygous for this allele?

When a species deviates from a 50:50 sex ratio (male to female) , 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. Which of the following processes most likely causes this pattern?

Which of the following statements best explains the need for the "2" in the 2pq term in the Hardy-Weinberg equation?

Which of the following statements about genetic variation is accurate?

Restriction enzymes in 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, they in turn select for bacteria whose genomes are not methylated and whose restriction enzymes instead degrade methylated DNA. Which of the following factors is most likely to cause the changes?

The value of the Hardy-Weinberg equation is that it allows scientists to perform which of the following assessments?

Over time, humans have steadily increased their movements across the continents of the Earth. Which of the following results has most likely been derived from these movements?

A species of moth lays eggs on oak trees in spring and summer. Spring caterpillars eat oak flowers and look like oak flowers. Summer caterpillars eat oak leaves and look like twigs. To investigate how the same population of moths can produce such variable caterpillars, a researcher collected eggs from a population of moths and allowed them to hatch and grow under the conditions shown in the table below. If day length causes the different development of caterpillars, which treatments will most likely produce twig-like caterpillars rather than flower-like caterpillars?

A researcher has maintained a small population of fruit flies in the laboratory by transferring the flies to a new culture bottle after each generation. After several generations, the viability of the flies decreased greatly. Recognizing that small population size is likely to be linked to decreased viability, which of the following approaches would be the best way to reverse this trend of decreased viability?

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. Which of the following events most likely occurred in the rodent populations following the accident?

In which of the following situations would genetic drift most likely cause evolution?

Which of the following is the best definition of evolution on the smallest scale?

If the nucleotide variability of a locus equals 0%, what is the gene variability and number of alleles at that locus?