Biology Assignment
Name
1. Imagine the following experiment on the scale-eating cichlid fish Perissodus microlepis. Three small artificial ponds
are established, each containing 100 of the cichlids and an abundant supply of common prey species. Pond A
contains 90 sinistral (left-handed) cichlids and 10 dextral (right-handed) cichlids. Pond B contains 50 of each type,
and Pond C contains 10 sinistrals and 90 dextrals. The relative frequency of the sinistral fish at the start of the
experiment is shown for each pond in the graph at right.
A. Based on what you know about these fish, predict the long-term changes (over the next 20 generations or so) in
the relative frequencies of sinistral fish in each of the three ponds and plot your predictions on the graph. You can
plot your predictions by double-clicking on the plot and then choosing the Scri
le tool under the Select line menu
(3 points).
B. Briefly explain your predictions in the space provided below (2 points).
C. Now imagine repeating the experiment described in (A)
with one important change; instead of having access to
living prey, the scale-eating cichlids are maintained on a
diet consisting exclusively of commercial fish food (Purina®
Scale Chow). Predict the long-term changes (over the
next 20 generations or so) in the relative frequencies of
sinistral fish in each of the three ponds and plot you
predictions on the graph. You can plot your predictions
y double-clicking on the plot and then choosing the
Scri
le tool under the Select line menu (3 points).
B. Briefly explain your predictions in the space provided
elow (2 points).
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2. Imagine that you are studying the meadow grasshopper Conocephalus whitenacki as your senior comp project.
Individuals of this species mate in early autumn and the females lay their eggs in the soil. The eggs hatch in May,
and the young grasshoppers emerge from the soil and feed on grasses and other meadow vegetation until they
each adult size and sexual maturity in August. Color pattern in these grasshoppers is determined by a single gene
locus with two alleles: BB homozygotes are
own, BG heterozygotes have longitudinal green and
own stripes,
and GG homozygotes are green. In a sample of 700 adult grasshoppers you collected from your study population in
late August, 140 were
own, 398 were striped, and 162 were green.
A. Assuming that your sample of 700 grasshoppers is representative of the entire adult population, estimate the
elative frequencies of the B and G alleles in the population. Show your work (2 points).
B. Calculate the expected genotype frequencies under the assumption that the population of grasshoppers is in
Hardy-Weinberg equili
ium, and compare the observed and expected genotype frequencies by calculating the
Chi-square statistic. Do they agree? (Hints: Chi-square statistic = χ2 = ∑ [(O - E)2 / E]; χ2 critical value = 3.84).
Show your work (3 points).
C. If you concluded that observed and expected genotype frequencies are in close agreement,
iefly explain what
this tells you about the population of grasshoppers you are studying. If you concluded that observed and
expected genotype frequencies are not in agreement, propose a single, specific hypothesis that would account
for the disagreement, and
iefly explain your hypothesis (2 points).
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D. Now imagine that you also analyze a sample of 390 young grasshoppers that you had collected earlier in the
season in late May, shortly after the young hatched from eggs. In this sample, 92 of the young grasshoppers were
own, 194 were striped, and 104 were green. Estimate the relative frequencies of the B and G alleles in this
sample, calculate the expected genotype frequencies under the assumption that the population of grasshoppers is
in Hardy-Weinberg equili
ium, and compare the observed and expected genotype frequencies by calculating the
Chi-square statistic. Show your work (5 points).
E. Now revisit your answer to parts (C) and (D) and try to reconcile them. In other words, do the data for young
grasshoppers (D) support or contradict the conclusions / hypothesis you made in part (C) for adult
grasshoppers? Briefly explain your reasoning (3 points).
3. The evolution of antibiotic resistance in disease-causing bacteria is a serious public health problem. Here is a
statement from the website drugs.com (https:
www.drugs.com/cg/antibiotic-resistant-bacteria.html) regarding the
issue: “When antibiotics are not used co
ectly, they may not kill all of the bacteria. The bacteria that an antibiotic
does not kill can grow stronger.” What is right and what is wrong with this statement? Briefly explain, and
provide a revised statement that portrays the evolution of antibiotic resistance more accurately and
effectively (5 points).
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https:
www.drugs.com/cg/antibiotic-resistant-bacteria.html
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4. In many species of beetles (for example, the forked fungus beetle Bolitotherus
cornutus shown at right), males have horn-like protuberances on their heads that are
absent in females.
A. Could horns in male forked fungus beetles be an example of a trait that has evolved
y intrasexual selection? Briefly explain how intrasexual selection could have led to
the evolution of horns, and
iefly explain how you could test this hypothesis (2
points).
B. Could horns in male forked fungus beetles be an example of a trait that has evolved by intersexual selection?
Briefly explain how intersexual selection could have led to the evolution of horns, and
iefly explain how you could
test this hypothesis (2 points).
C. In the population of forked fungus beetles around Meadville, you find continuous variation in male horn length;
most males in the population have average-length horns, but some have horns that are considerably longer o
shorter than average. Briefly describe the two ways you could determine if this variation in male horn length has a
heritable genetic basis (2 points).
5. The three-spined stickleback is a species of fish in which males in
eeding condition
have
ight red bellies. Laboratory and field experiments have shown that females strongly
prefer to mate with males with the very reddest bellies. Would you therefore be justified in
concluding that males of future generations of sticklebacks will have bellies that are even
edder than those of present-day males? Briefly explain why or why not (4 points).
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6. Imagine that you are studying the sky pilot
Polemonium viscosum, a small insect-pollinated
alpine plant of the southern Rocky Mountains. About
15,000 years ago during the last ice age, this species
existed in one continuously distributed population at
lower elevations on the slopes of Mt. French and Mt.
Venesky, two of the more imposing peaks of the
southern Rockies. As the earth has warmed over the
last 15,000 years, however, the elevational range of
the species has shifted upward; now sky pilots exist
only in two isolated and genetically distinct
populations at the summits of the two mountains.
The shaded regions in the figure at right reflect the
past and cu
ent distribution of the species.
A. What two evolutionary processes are most likely to be responsible for the genetic differences that now exist
etween the Mt. French and Mt. Venesky population of sky pilots? Briefly explain (2 points).
B. Could the sky pilot populations on Mt. French and Mt. Venesky eventually evolve into two separate sky pilot
species? Briefly explain (1) what conditions would be necessary for speciation to occur, and (2) what type of
speciation process is most relevant to this situation (3 points).
C. On Mt. French, sky pilots are very common and the population size is cu
ently very large (>10,000 plants). On
Mt. Venesky, however, sky pilots are quite rare, and the total population is cu
ently fewer than 500 plants. Based on
this information, which of the two populations of sky pilots is likely to be genetically most different from the
"ancestral" population of sky pilots that was continuously distributed around the two mountains 15,000 years ago?
Briefly explain (2 points).
D. Now fast-forward 15,000 years — after the coming
zombie apocalypse, attack of the murder hornets, and
ule of the Night King — to a future post-apocalyptic
ice age. Imagine that cooling of the earth’s climate and
glaciation at higher elevations creates conditions that
allow the two sky pilot populations to spread down
from their respective mountain tops and rejoin on the
slopes beneath the two peaks (see shaded regions in
the figure at right). Using the Biological Species Concept as your guide, how could you determine whether the Mt.
French sky pilot and Mt. Venesky sky pilot should be recognized as two distinct species? Briefly explain how you
could make this assessment (3 points).
Congratulations! You are done! Best wishes for the holidays and the New Year!