Test Prep for AP® Courses
A scientist is studying the genetics of a population of plants that she suspects is undergoing natural selection. After examining samples of the population’s DNA over several years, she finds the following data.
|Allele A Frequency
|Allele B Frequency
Does this provide evidence of natural selection in this population? Why or why not?
- No, because the genotype frequencies, not allele frequencies, have to change for evolution to occur.
- No, because the allele frequencies are changing randomly, suggesting that genetic drift is occurring, not natural selection.
- Yes, because it shows that the previously favorable or neutral allele A is now being selected against in favor of allele B.
- Yes, because it is showing that the frequency of both alleles are changing over time.
A scientist is studying two large populations of deer that are centralized in nearby forests. She takes blood samples from all of the deer in each population and records in how many individuals she finds allele A. She then computes the frequency of the alleles in each population. The frequencies observed over five years are shown in the tables below.
Which forms of evolution are most likely occurring in populations A and B? Explain your answer.
- In population A, genetic drift is likely occurring, causing allele A to become more prevalent than allele B. In population B, mutation apparently occurred, introducing allele A to population B. Allele A also appears to be increasing due to genetic drift in population B.
- In population A, natural selection is likely occurring, with allele A being favored over allele B. In population B, gene flow apparently occurred, allowing allele A to become established in population B. Allele A also appears to be favored by selection in population B.
- In population A, gene flow apparently occurred, allowing allele B to become established in population A. Allele A also appears to be favored by selection in population A. In population B genetic drift is likely occurring, causing allele A to become more prevalent than allele B.
- In population A, mutation apparently occurred, introducing allele B to population A. Allele A also appears to be increasing due to genetic drift in population A. In population B natural selection is likely occurring, with allele A being favored over allele B.
A land manager mows a section of annual grass at the end of July. Over the years, he recorded the date of flowering from the mown field as well as a similar grass field that was not mown. What is the most likely explanation for this trend?
|Mowed Field Flowering Date
|Unmowed Field Flowering Date
- Mowing stimulates flowering, so the grass adapts by flowering after mowing occurs.
- Mowing stabilizes the flowering time, which follows a steady trend in the mowed field but not in the unmowed field.
- The mowing is preventing the grass from reproducing, causing the mowed field to adapt by flowering earlier.
- The grass typically flowers earlier and earlier every year as it becomes older with each passing year.
A scientist observed two populations of insects for 10 years. They took data on the length, in mm , of the insect’s mouthparts. Their data is shown in the graphs below.
- Inbreeding, because the gene distributions are becoming less similar among the population.
- Genetic drift, as the distribution of traits has become more random.
- Gene flow, as the population has likely gained new mouthpart traits through immigration.
- Natural selection, as insects that have mid-sized mouthparts are being favored.
Researchers believe that in a fish species, individuals with the recessive genotype aa are predisposed to disease. Homozygous dominant (AA) individuals and heterozygous (Aa) individuals are not believed to be susceptible to this disease. A pond was stocked with 100 fish of the AA genotype and 100 fish of the aa phenotype, and the fish were allowed to breed. In the next generation, 35 percent of the fish had the dominant (AA) phenotype. What does this result indicate?
- The homozygous dominant phenotype is higher than expected, indicating that evolution has occurred.
- The homozygous dominant phenotype is lower than expected, indicating that evolution has occurred.
- The homozygous dominant phenotype is higher than expected, indicating that evolution has not occurred.
- The homozygous dominant phenotype is lower than expected, indicating that evolution not occurred.
- It would remain in equilibrium because the value of and would remain the same.
- It would remain in equilibrium because the value of would remain the same.
- It would not remain in equilibrium because the value of would likely increase.
- It would not remain in equilibrium because the value of would likely decrease.
The graph below shows the change in gene frequency of the two alleles of a gene: A and a. The population being studies has no emigration or immigration. Which type of evolution is likely occurring here and is the allele selected for, neutral, or selected against by natural selection?
- nonrandom mating; both alleles are favored
- gene flow; allele A is favored
- genetic drift; both alleles are neutral
- natural selection; allele a is not favored
The figure below shows the change in gene frequency of the two alleles: A and B. These alleles are located on separate genes that do not influence each other in any way. The population being studied has no emigration or immigration. Which type of evolution is likely occurring here, if at all? Explain how you know.
The graph below shows the current frequencies of two genotypes of the same gene: AA and aa. What would most likely happen to the frequencies of A and a if heterozygous individuals were favored by natural selection?
- Both AA and aa will drop in frequency by the same amount.
- Both AA and aa will drop, but aa will drop more.
- AA will increase in frequency and aa will drop in frequency.
- Genotype aa will increase in frequency and AA will drop in frequency.
The diagram below shows the frequency of alleles on two species of wind-pollinated plants, as well as the prevailing wind direction. These frequencies have been fairly stable for around 10 years. However, climate change has created a new prevailing wind direction, as shown in the diagram. How will the two populations likely evolve in the future?
- Natural selection will cause the frequency of B to increase in population 1.
- Gene flow will cause the frequencies of A and B to drop in population 3.
- Genetic drift will cause the frequencies of A and C to increase in population 1 and 2.
- Inbreeding will reduce the frequency of allele B in population 2 and 3.
The diagram shows two populations of a species that have been long-separated by a river, which prevents interbreeding. The two populations differ in coloration, as shown in the diagram. Recent human activity has caused the river to dry, however, resulting in the two populations shown in the lower diagram. What is the most likely explanation for this change?
- an increase in gene flow between the two populations
- a decrease in gene flow between the two populations
- an increase in nonrandom mating between the two populations
- a decrease in nonrandom mating between the two populations
Antibiotics are medicines that are designed to kill disease-causing organisms, or pathogens. However, some pathogens evolve antibiotic resistance, where they gain traits that allow them to survive in the presence of antibiotics. The ability of bacteria to adapt to antibiotics so quickly has created a huge concern over whether antibiotics are being overused. What form of evolution is antibiotic resistance an example of, and why?
- gene flow because the bacteria are passing on the resistant trait within their populations
- natural selection, because the bacteria is adapting to a new environmental condition: the presence of the antibiotic
- genetic drift because medical workers cannot follow the randomly-fluctuating gene frequencies of bacterial populations
- mutation, because each bacteria must mutate to an antibody-resistant form in order to survive