Population Genetics and H-W (Unit 7 Standard B) Reading Quiz

In humans, one allele of the  APOE gene, called  APOE–ε2 , can result in a high tolerance of cholesterol. Cholesterol is a vital substance for humans but may lead to heart disease in an older adult with a history of high cholesterol diets. High cholesterol diets are becoming more prevalent in the United States. Currently only about 2% of humans carry the  APOE–ε2 allele.

Which of the following states a valid null hypothesis about the future distribution of  APOE alleles in future generations in the United States?

• The  APOE–ε2 allele was the result of chance mutations so it is not possible to predict how its frequency will change in the future.

• As high cholesterol diets become more common in the United States, individuals with the  APOE–ε2 allele will have a better survival rate from heart disease than those without the allele, so the allele will increase in frequency.

• The low frequency of the  APOE–ε2 allele indicates it is probably a recessive allele, so it will become less frequent as the dominant allele becomes more frequent.

• The variant protects an individual from a condition that is only common among humans beyond reproductive age, so the frequency of the allele will likely not change much in the future because it is not influenced by natural selection.

Students observed the distribution of different color phenotypes in northern ravine salamanders (Plethodon electromorphus) before and after a spring flood. The data are shown in Table 1.  Which of the following is an appropriate null hypothesis regarding the phenotypic frequencies of this population of salamanders before and after the flood?

• More black salamanders survived because they could better hide from predators on the dark muddy soil, so the frequency of the black phenotype significantly increased in the population after the flood.

• Fewer light-brown salamanders survived because they had a reduced chance of finding mates due to the high water levels, so the frequency of the light-brown phenotype in the population decreased after the flood.

• The proportions of black, dark-brown, and light-brown salamanders before and after the flood are not significantly different, and any observed differences are due to random chance.

• More dark-brown salamanders migrated to a new, drier area because of the flood and fewer of them remained in the original habitat, so the frequency of dark-brown salamander significantly decreased in the population after the flood.

The California newt, Taricha torosa, lives in the coastal areas around Los Angeles. Which of the following is a valid null hypothesis relating fitness to survival of a bottleneck event in a coastal area where a small, isolated population of California newts resides?

• Only those salamanders with the lowest evolutionary fitness will be eliminated by the bottleneck effect, lowering the allelic frequencies of their traits.

• Only those salamanders with the highest evolutionary fitness will survive the bottleneck event, raising the allelic frequencies of their traits.

• Surviving the bottleneck event will be random, so any change in the allelic frequencies of the salamander population is not attributed to fitness.

• Surviving the bottleneck event will be random, so there will be no changes to the allelic frequencies due to the bottleneck event.

In eastern gray squirrels, Sciurus carolinensis, the allele for black fur  (B) is dominant to the allele for gray fur  (b). In a particular population of gray squirrels, 64% have black fur and 36% have gray fur. A researcher calculated the allelic frequencies to be  B=0.4 and  b=0.6. Five years later, the researcher returned to the location and determined the allelic frequencies within the squirrel population to be  B=0.6 and  b=0.4.   Which of the following could best explain the increase in the frequency of the  B allele in the population after five years?

• The frequency of the  B allele increased because it is the dominant allele.

• The frequency of the  B allele increased because squirrels with gray fur exhibited greater fitness.

• The frequency of the  B allele increased due to the selective pressures of the environment.

• The frequency of the  B allele increased because black squirrels randomly mate with other eastern gray squirrels.

Gaucher disease type 1 ( GD1 ) is a recessive genetic disease that affects 1 in 900 individuals in a particular population.  GD1 is caused by a mutation in the enzyme glucocerebrosidase.

Assuming the population is in Hardy-Weinberg equilibrium, calculate the frequency of the wild-type (nonmutant) allele for the enzyme glucocerebrosidase.

• 0.001

• 0.033

• 0.967

• 0.999

In a long‑term study of a population of gray squirrels, researchers observed that most of the squirrels had gray fur. However, there were some individuals in the population with white fur (albino). Genetic analysis revealed that the albino condition is expressed by individuals who are homozygous recessive  (gg) . Over a ten-year period, the average frequency of albino squirrels in the population was 0.18. If the population is assumed to be in Hardy-Weinberg equilibrium, the average frequency of the dominant allele is closest to which of the following?

• .42

• .50

• .58

• .75

In a large, isolated population of an insect species, a specific gene locus has one dominant allele  (A)

  and one recessive allele  (a). The genotype frequencies of the gene were collected for ten generations, as shown in Table 1. Which of the following could best account for the change in genotypic frequencies over the ten generations?

• Because the  A  allele is unstable, over the course of the study most of the  A alleles mutated to become  a alleles.

• The population is in Hardy-Weinberg equilibrium, which allows for changes in genotypic frequencies every generation.

• The population is not exhibiting random mating between individuals.

• The population is becoming extinct because the  a  allele is disappearing.

Which of the following statements best explains how a condition of Hardy-Weinberg equilibrium results in a population that exhibits stable allele frequencies (i.e., a nonevolving population) ?

• Large populations are not subject to natural selection.

• Random mating prevents gene flow from changing allele frequencies.

• Without migration or mutation, new alleles cannot be introduced to the population.

• In the absence of selection, allele frequencies in a population will not change.

 Humans vary in their ability to taste the bitter chemical compound phenylthiocarbamide ( PTC ). The taster phenotype is dominant to the nontaster phenotype. Researchers tested the  PTC  taster phenotype of individuals from an isolated population. In the sample, 780 individuals were able to taste  PTC  and 70 individuals were not able to taste  PTC.

Assuming the population is in Hardy-Weinberg equilibrium, what is the frequency of the non-taster allele?

• .08

• .29

• .41

• .71