1.5 b: variation and fitness quiz proctor version · 2016. 5. 1. · (b) the male peacocks with...

1. Two species of chipmunk are being studied in a national park. The alpine chipmunk lives on the

tops of mountain ranges, and the lodgepole chipmunk lives in lower forested areas. The historic

and modern ranges of the two species are shown in the maps below.

DNA samples from specimens preserved in 1910 and living individuals for both species are

tested. The results are shown in the table below.

1.5 B: Variation and Fitness Quiz

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Which choice identifies the chipmunk species with the highest overall fitness and best explains

the difference in fitness observed in the two populations?

(A) The alpine chipmunk, because it has moved into a smaller area where the selective

pressures are similar, and therefore, a smaller set of alleles has been required for survival,

whereas the lodgepole chipmunk has maintained a large habitat with many niches, so

natural selection supports a wide variety of alleles

Distractor Rationale:

This answer suggests the student may understand that a large range promotes greater

genetic diversity, but does not understand that this explanation is not supported by the

data, because there is no evidence that a smaller range for the alpine chipmunk implies

fewer selective pressures on that population.

(B) The lodgepole chipmunk, because it has spread into the habitat originally held by the alpine

chipmunk, and this increased competition has reduced the number of available niches and

the population size of the alpine chipmunk, which has resulted in a loss of genetic diversity


This answer suggests the student may understand that competition from a new species can

cause population declines, but does not understand that this explanation is not supported

by the data, because the lodgepole chipmunk’s range has stayed relatively the same

according to the maps.

(C) The alpine chipmunk, because it had been competing with the lodgepole chipmunk for the

same resources due to the two species sharing the same fundamental niche, and through

this competition, the alpine chipmunk has adopted a smaller niche that requires less genetic

diversity than its original habitat


This answer suggests the student may understand that direct competition with another

species can reduce genetic diversity and population size, but does not understand that this

explanation is not supported by the data, because the evidence provided indicates that the

two chipmunks occupy different niches based on altitude.

(D) The lodgepole chipmunk, because the alpine chipmunk has suffered significant loss in

habitat, resulting in a smaller population size with less genetic diversity than the original

population, whereas the lodgepole chipmunk has maintained a relatively large population

and therefore retains a high genetic diversity


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Rationale:

This answer suggests the student understands that the maps show a major shift in the

habitat range of the alpine chipmunk and that this most likely indicates a decrease in both

population size and genetic diversity, and that, because the fitness of a population depends

on the diversity of the alleles present in the population and a smaller population will usually

have less genetic diversity, the alpine chipmunk would likely have a lower overall fitness

than the lodgepole chipmunk.

Aligned to: LO 1.5 CA 1.5: Impact of Environment on Evolution

2. Polychlorinated biphenyls (PCBs) are toxic, man-made compounds found at high levels in some

rivers and bays in the United States. PCBs bind to a protein called AHR, which initiates the

transcription of genes in the nucleus and produces a toxic buildup of unnecessary proteins. In

rivers that have high levels of PCBs, some tomcod fish have been found to have a small deletion

in the gene that codes for the AHR protein; this deletion prevents PCBs from binding to the

protein. This mutation is high in tomcod populations that live in contaminated rivers, but is rare or

nonexistent in fish that live in other rivers.

The map below shows the relative frequency of the gene in different tomcod populations. The

white part of the pie chart for the tomcod population in each river or bay shows the proportion of

the population that has the gene deletion, and the black part of the pie chart shows the proportion

of the population that does not have the gene deletion.

Which statement describes the most likely outcome if tomcod with the deletion in the AHR gene

are introduced into other rivers in New England?


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(A) The gene frequency of the AHR mutation will remain low in all tomcod populations where the

tomcod with the mutation are introduced, because this mutation is only beneficial in the

Hudson and Hackensack Rivers, so there is no selective advantage to having the mutation

in other rivers.


This answer suggests the student may understand that the mutation is only beneficial in

rivers containing PCBs, such as the Hudson and Hackensack Rivers, but does not

understand that the mutation may also allow for a selective advantage in other rivers with

PCB contamination because the mutation would convey resistance to the toxic effects of

PCBs in these areas as well.

(B) The gene frequency of the AHR mutation will remain low in populations of tomcod fish where

there is no PCB contamination, but will become more prevalent in rivers that have PCB

contamination, because the populations of tomcod that contain the AHR mutation will have a

selective advantage.

Rationale:

This answer suggests the student understands that the AHR mutation frequency will

increase only in rivers with PCB contamination but will remain low in non-contaminated

rivers because there will be no selective advantage to having the AHR gene mutation.

(C) The gene frequency of the AHR mutation will increase in all tomcod populations where the

tomcod with the mutation are introduced, because the mutation allows fish to tolerate toxins,

such as PCBs, and therefore provides a selective advantage to tomcod that have the

mutation in the populations.


This answer suggests the student may understand that the mutation conveys a selective

advantage in PCB-contaminated rivers, but does not understand that the gene frequency

may not increase in non-contaminated rivers because this mutation may be selected against

in the absence of PCBs.

(D) The gene frequency of the AHR mutation will decrease and eventually disappear in all

tomcod populations where the tomcod with the mutation are introduced, because this

mutation is only beneficial in the Hudson and Hackensack Rivers and will be a disadvantage

in tomcod populations not found in these two rivers.


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This answer suggests the student may understand that the mutation is beneficial in the

Hudson and Hackensack Rivers, which contain PCBs, but does not understand that the

mutation may also allow for a selective advantage in other rivers with PCB contamination

because the mutation would convey resistance to the toxic effects of PCBs in these areas as

well.


3. There is variation in the size and brightness of the color of male peacocks’ tails. A peacock

population is observed in the wild, and the color and length of the male peacocks’ tails are noted.

The males are then tracked, and their percentages of total matings and their average life spans

are recorded. The data are shown below.

Based on the data, which is the best explanation of the evolutionary fitness of male peacocks?

(A) The male peacocks with long, more colorful tails are more fit because they are able to mate

with more females during their life spans.

Rationale:

This answer suggests the student understands that the data in the graph and table support

that male peacocks with long, colorful tails have a higher evolutionary fitness due to the

higher frequency of mating and despite the difference in average life span, because

reproductive success is the main component of evolutionary fitness, and that male peacocks

with long, colorful tails mate more frequently than male peacocks with short, less colorful

tails. The student is able to connect genotypic variation, differences in the length and color

of the male peacocks’ tails, with the different degrees of fitness.


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(B) The male peacocks with long, more colorful tails are more fit because they are healthier and

able to grow longer tails with brighter coloration.


This answer suggests the student may understand that producing long, brightly colored tail

feathers is a sign of health, but does not understand that fitness is ultimately about

reproductive success, and not just survival, because reproduction is what allows for the

passage of genes in the population.

(C) The male peacocks with short, less colorful tails are more fit because they have longer

average life spans.


This answer suggests the student may understand that survival is important in determining

fitness, but does not understand that fitness is ultimately about reproductive success, and

not just survival, because reproduction is what allows for the passage of genes in the

population.

(D) The male peacocks in the two groups have about the same level of fitness because the

males with long, more colorful tails have more reproductive success and the males with

short, less colorful tails have higher rates of survival.


This answer suggests the student may understand that survival and reproductive success

are both important, but does not understand that fitness is ultimately about reproductive

success, and not just survival, because reproduction is what allows for the passage of genes

in the population.



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4. In the 1990s, the Florida panther population had decreased to several dozen individuals, and

scientists predicted that the Florida panther would be extinct by 2015. In 1995, conservationists

introduced eight female panthers from Texas to the population. Between 1995 and 2003, the

Texas panthers bred with native Florida panthers, and now there are more than one hundred

panthers in South Florida. Before the introduction, biologists identified genetic markers of two

ancestral lines (descendants from a common relative). In 2007, genetic analysis revealed five

ancestral lines, as shown in the maps below.

Which statement best explains the changes in phenotypic variation and relative fitness of the

Florida panther population after the introduction of the Texas panthers?

(A) The phenotypes of the introduced panthers were better adapted to the environment than the

phenotypes of the Florida panthers, so the introduced genes replaced the original ancestral

genes because natural selection favored the introduced alleles.


This answer suggests the student may understand that when new alleles are introduced into

a population through gene flow, these alleles can increase in frequency if the alleles offer a

selective advantage, but does not understand that, in this case, the new alleles did not

completely overtake the existing alleles, but instead, they increased the relative fitness of

the existing population because the new alleles increased the genetic diversity in the

existing gene pool.

(B) The phenotypes of the introduced panthers were better adapted to the environment than the

phenotypes of the Florida panthers, so the introduced panthers started to drive the Florida

panthers to extinction because the panthers with the new alleles had a higher fitness.


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This answer suggests the student may understand that when new alleles are introduced into

a population through gene flow, these alleles can increase in frequency if the alleles offer a

selective advantage, but does not understand that, in this case, the new alleles did not

completely overtake the existing alleles and drive the original Florida panthers to extinction,

but instead, they increased the relative fitness of the existing population because the new

alleles increased the genetic diversity in the existing gene pool.

(C) The introduced panthers provided new alleles to the population, which increased the

evolutionary fitness of the Florida panther population because natural selection favored the

introduced alleles over the original ancestral genes.


This answer suggests the student may understand that new alleles were introduced into the

population and that these new alleles increased the relative fitness of the population, but

does not understand that this increased relative fitness is due to the additional genetic

diversity that the new alleles provided, not because natural selection necessarily favored the

introduced alleles over the original ancestral genes.

(D) The introduced panthers provided new alleles to the population, which increased the

evolutionary fitness of the Florida panther population because the new alleles increased

genetic diversity and phenotypic variation in the population.

Rationale:

This answer suggests the student understands that when the Texas panthers were

introduced into the population, they increased the relative fitness of the population because

they increased genetic diversity by introducing new alleles into a population with low genetic

diversity.



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1.5 b: variation and fitness quiz proctor version · 2016. 5. 1. · (b) the male peacocks with...

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