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Name:
Interpreting Evolutionary Data
Brown bear
7
Polar bear
American black bear
4
5
6
3
2
1
Asian black bear
Sun bear
Sloth bear
Spectacled bear
Giant panda
1. First, practice reading the phylogenetic relationships from the tree. Which number
represents the most recent common ancestor of:
a. All bears
b. Sloth bears and spectacled bears
c. The Asian black bear and the American brown bear
d. According to the data represented in this tree, is the sun bear more closely related to
the sloth bear or the polar bear? Explain.
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2. Seven different organisms and six different traits are show in the table. Draw a phylogenetic
tree based on characters 1-5 in the table. Place hatch marks on the tree to indicate the
origins of characters 1-6.
Character
1. Backbone
2. Hinged jaw
3. Four limbs
4. Amnion
5. Milk
6. Dorsal (back) fin
Lancelet
(outgroup)
0
0
0
0
0
0
Lamprey Tuna Salamander
1
0
0
0
0
0
1
1
0
0
0
1
1
1
1
0
0
0
Turtle Leopard
1
1
1
1
0
0
Dolphin
1
1
1
1
1
0
3. Is Evolution occurring in a soybean population?
One way to test whether evolution is occurring in a population is to compare the observed
genotype frequencies with those expected for a nonevolving population based on the HardyWeinberg equation. In this exercise you will test whether a soybean population is evolving at a
locus (locus = location on a chromosome) with 2 alleles CG and CY that affect chlorophyll
production and hence leaf color.
How the experiment was done: Students planted soybean seeds and then counted the number
of seedlings of each genotype at day 7and again at day 21. Seedlings of each genotype could be
distinguished visually because the CG and CY alleles show incomplete dominance: CGCG seedlings
1
1
1
1
1
1
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have green leaves and CGCY seedlings have green-yellow leaves, and CYCY seedlings have yellow
leaves.
Data from experiment:
Number of Seedlings
Time
(Days)
Green
(CGCG)
Green-yellow
(CGCY)
Yellow
(CYCY)
Total
7
49
111
56
216
21
47
106
20
173
a. Use the observed genotype frequencies from day 7 data to calculate the frequencies of
the CG allele (p) and the CY allele (q).
b. Next use the Hardy-Weinberg equation p2 + 2pq + q2 = 1 to calculate the expected
frequencies of genotypes CGCG, CGCY, and CYCY for a population in Hardy-Weinberg
equilibrium.
c. Calculate the observed frequencies of genotypes CGCG, CGCY, and CYCY at day 7. (The
observed frequency of a genotype in a gene pool is the number of individuals with that
genotype divided by the total number of individuals.) Compare these frequencies to the
expected frequencies calculated in part b. Is the seedling population in Hardy-Weinberg
equilibrium at day 7, or is evolution occurring? Explain your reasoning and identify
which genotypes, if any, appear to be selected for or against.
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d. Calculate the observed frequencies of genotypes CGCG, CGCY, and CYCY at day 21.
Compare these frequencies to the expected frequencies in part b and the observed
frequencies at day 7. Is the seedling population in Hardy-Weinberg equilibrium at day
21, or is evolution occurring? Explain your reasoning and identify which genotypes, if
any, appear to be selected for or against.
e. Homozygous CYCY individuals cannot produce chlorophyll. The ability to
photosynthesize becomes more critical as seedlings age and begin to exhaust the supply
of food that was stored in the seed from which they emerged. Develop a hypothesis
that explains the data for days 7 and 21. Based on the hypothesis, predict how the
frequencies of the CG and CY alleles will change beyond day 21.
4. Does distance between salamander populations increase their reproductive isolation?
The process of allopatric speciation begins when populations become geographically isolated,
preventing mating between individuals in different populations and thus stopping gene flow. It
seems logical that as distance between populations increases, so will their degree of
reproductive isolation. To test this hypothesis, researchers studied populations of the dusky
salamander living on different mountain ranges in the southern Appalachian Mountains.
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How the experiment was done: The researchers studied the reproductive isolation of pairs of
salamander populations by leaving one male and one female together and later checking on the
females for the presence of sperm. Four mating combinations were tested for each pair of
populations (A & B) — two within the same population (female A with male A and female B
with male B) and two between populations (female A with male B and female B with male A).
Data from the experiment: The researchers used an index of reproductive isolation that ranged
from a value of 0 (no isolation) to a value of 2 (full isolation). The proportion of successful
matings for each mating combination was measured, with 100% success = 1 and no success = 0.
The reproductive isolation value for two populations is the sum of the proportion of successful
matings of each type within populations (AA+BB) minus the sum of proportion of successful
matings of each type between populations (AB+BA). The following table provides data for 27
pairs of dusky salamander populations.
Geographic Distance
(km)
15
32
40
47
42
62
63
81
86
107
107
115
137
147
Reproductive Isolation
Value
.32
.54
.50
.50
.82
.37
.67
.53
1.15
.73
.82
.81
.87
.87
Geographic Distance
(continued)
137
150
165
189
219
239
247
53
55
62
105
179
169
Reproductive Isolation
Value (continued)
.50
.57
.91
.93
1.50
1.22
.82
.99
.21
.56
.56
.72
1.15
a. State the researchers’ hypothesis, and identify the independent and dependent
variables in this study. Explain why the researchers used four mating combinations for
each pair of populations.
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b. Make a scatter plot of one variable against the other to help you visualize whether or
not there is a relationship between the variables.
c. Interpret your graph by explaining in words the relationship between the variables that
can be visualized by graphing the data.