Molecular clock tutorial assignment worksheet
Student number ___________________
Part 1 [24]
1. Explain why the number of differences between lineages may not be the same as the sum of the number of
substitutions in each lineage at a given time period (look at 5, 10 and 15 Ma)?
(3)
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2. a. Complete the Table with the ​mean and variance of number of substitutions at each of the three time
periods (5, 10 and 15 Ma) for the left and the right lineage. [See Appendix A-2 of the textbook for calculating
means and variances]
(6)
Simulations 5 Mil
5 Mil
10 Mil 10 Mil 15 Mil 15 Mil
Left
Right
Left
Right
Left
Right
lineage lineage lineage lineage lineage lineage
1
5
5
9
14
21
11
2
5
3
10
11
10
16
3
4
3
9
10
17
13
4
4
4
11
7
10
14
5
8
4
7
14
14
10
6
2
0
8
12
19
10
7
4
4
10
13
17
12
8
6
4
9
9
16
12
9
4
8
9
8
16
18
10
5
9
8
8
14
13
Mean:
Variance:
b. Are the means and variances the same between the two lineages? Explain.
(2)
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3. Draw/insert a graph of the means (numbers of substitutions only) at 5, 10 and 15 Ma for each of the two
lineages independently. Remember time is on the X-axis.
(4)
4. Based on the data, calculate the mean substitution rate per nucleotide per million years. Remember there
are 100 nucleotides in the sample.
(3)
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5. Based on your substitution rate estimate, how many substitutions would you predict will accumulate
between the ancestral and each descendant lineage in 50 million years?
(2)
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6. Compare the predicted number of substitutions in question 5, to the observed substitutions from the 10
simulations at 50 Ma. Explain your observation.
(2)
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7. What happens when we take into account multiple substitutions at a site? Answer this based on the
information provided for the 10 simulations at 50 Ma.
(2)
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