Which is the most likely explanation for the trend in the frequencies of the two alleles?

Frequency dependent selection will also occur with the gene-for-gene relationship that determines pathogenicity (p. 256).

From: The Fungi (Third Edition), 2016

Consider a polymorphic gene with three alleles: A, B, and C.A. If the frequencies of the alleles A and B are 0.2 and 0.3, the frequency of allele C is closest to ___.a. 0.25b. 0.5c. 0.2d. 0.3Consider a gene with only two alleles: dominant A and recessive a. In a population of 1,000 organisms, the fraction expressing the homozygous recessive phenotype is 0.37.B. The calculated allele frequencies p and q have values that are closest to ___.a. 0.69 and 0.31b. 0.31 and 0.69c. 0.37 and 0.63d. 0.63 and 0.37C. The calculated number of individuals in this population that are heterozygotes is closest to ___.a. 240b. 230c. 430d. 476Mountain pine beetles (Dendroctonus ponderosae) were collected from a one-acre tract of lodge pole pine trees (Pinus contorta) in a region of British Columbia where the forests are under temperature stress. The beetles were crushed, and a cellulase enzyme was extracted. Three polymorphs of the enzyme were observed when separated by gel electrophoresis. The three proteins observed correspond to alleles labeled C1, C2, and C3. The numbers of beetles with each allele are shown in the following table.D. The calculated allelic frequencies pC1, pC2, and pC3 are closest to ___.a. $\quad \mathrm{P_{Cl}}=0.57 \mathrm{P_{C2}}=0.57 \mathrm{P_{C3}}=0.59$b. $\quad \mathrm{P_{Cl}}=0.29 \mathrm{P_{C2}}=0.29 \mathrm{P_{C3}}=0.42$c. $\quad \mathrm{P_{Cl}}=0.61 \mathrm{P_{C2}}=0.80 \mathrm{P_{C3}}=0.59$d. $\quad \mathrm{P_{Cl}}=0.31 \mathrm{P_{C2}}=0.40 \mathrm{P_{C3}}=0.29$E. In order to investigate the presence of selection at the cellulase locus due to changing temperature, a biologist should:a. calculate the values of the sums $\mathrm{P_{Cl}}+\mathrm{P_{C2}}+\mathrm{P_{C3}}+$ and $(\mathrm{P_{Cl}}+\mathrm{P_{C2}}+\mathrm{P_{C3}}+)^{2}$.If these numbers are not equal to 1, the gene is not in Hardy-Weinberg equilibrium, and the gene is evolving.b. return next year and repeat this examination of the enzyme, calculating frequencies of each allele each year. Then calculate the values of the sums $\mathrm{P_{Cl}}+\mathrm{P_{C2}}+\mathrm{P_{C3}}+$ and $(\mathrm{P_{Cl}}+\mathrm{P_{C2}}+\mathrm{P_{C3}}+)^{2}$ . If these numbers are not the same each year, the gene is not in Hardy-Weinberg equilibrium, and the gene is evolving.c. return each year for several years and repeat this examination of the enzyme, calculatingfrequencies of each allele each year. If the allele frequencies are changing, the gene is not in Hardy-Weinberg equilibrium, and temperature is exerting a selection pressure.d. return each year for several years and repeat this examination of the enzyme, calculating

frequencies of each allele each year. If the allele frequencies are changing, the gene is not in Hardy-Weinberg equilibrium. Analysis of the dependence of allele frequencies on temperature could indicate selection.

29.

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:

Year	Allele A Frequency	Allele B Frequency
1	0.80	0.2
2	0.72	0.28
3	0.66	0.34
4	0.52	0.48
5	0.45	0.55
6	0.39	0.61

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.

30.

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 allele frequencies observed over five years are shown in the tables provided. Evaluate the data to answer the following: Which forms of evolution are most likely occurring in populations 1 and 2? Provide evidence to support your answer.

Population 1
Year	Allele A Frequency	Allele B Frequency
1	0.69	0.31
2	0.71	0.29
3	0.73	0.27
4	0.75	0.25
5	0.81	0.19
6	0.84	0.16

Population 2
Year	Allele A Frequency	Allele B Frequency
1	0.00	1.00
2	0.00	1.00
3	0.10	0.90
4	0.16	0.84
5	0.21	0.79
6	0.25	0.75

In population 1, genetic drift is likely occurring, causing allele A to become more prevalent than allele B. In population 2, a mutation apparently occurred, introducing allele A to population 2. Allele A also appears to be increasing due to genetic drift in population 2.
In population 1, natural selection is likely occurring, with allele A being favored over allele B. In population 2, gene flow apparently occurred, allowing allele A to become established in population 2. Allele A also appears to be favored by selection in population 2.
In population 1, gene flow apparently occurred, allowing allele B to become established in population 1. Allele A also appears to be favored by selection in population 1. In population 2, genetic drift is likely occurring, causing allele A to become more prevalent than allele B.
In population 1, mutation apparently occurred, introducing allele B to population 1. Allele A also appears to be increasing due to genetic drift in population 1. In population 2, natural selection is likely occurring, with allele A being favored over allele B.

31.

A land manager mows a section of annual grass. 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?

Year	Mowed field flowering date	Unmowed field flowering date
2010	7/29	7/28
2011	7/20	7/26
2012	7/13	8/1
2013	7/8	7/29
2014	7/1	8/2
2015	6/29	7/26

The grass population is adapting to the mowing, so it can flower for longer before being mowed.
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.

32.

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. How is this population evolving and what agent of evolution is most likely at work?

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

33.

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 has not occurred.

34.

Heterozygote advantage is a condition in which heterozygotes in a population are favored by natural selection. Predict how the value of 2pq would likely change if a population was undergoing heterozygote advantage.

It would remain in equilibrium because the values of p and q would remain the same.
It would remain in equilibrium because the value of 2pq would remain the same.
It would not remain in equilibrium because the value of 2pq would likely increase.
It would not remain in equilibrium because the value of 2pq would likely decrease.

35.

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?

non-random mating; both alleles are favored
gene flow; allele A is favored
genetic drift; both alleles are neutral
natural selection; allele a is not favored

36.

The graph 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.

no multiple choice available
no multiple choice available

37.

The graph pictured shows the current frequencies of two genotypes of the same gene: AA and aa. Analyze the graph to predict which of the following would most likely happen to the frequencies of the two genotypes 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 in frequency, but aa will drop more.
AA will increase in frequency and aa will drop in frequency.
aa will increase in frequency and AA will drop in frequency.

38.

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

39.

The diagram below shows two populations of organisms 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 non-random mating between the two populations
a decrease in non-random mating between the two populations

40.

(credit: modification of work from APS Press)

Triadimenol is a fungicide used in agriculture. The graph shows the resistance of a type of fungus to this chemical over time. Each line in the graph represents data from a different year.

Describe the pattern seen here.

The fungus population did not change over time.
The fungus developed resistance to the fungicide over time due to directional selection.
The fungus becme more susceptible to the fungicide over time due to stabilizing selection.
The fungus became more susceptible to the fungicide over time due to unknown reasons.