Lab: The Molecular Connection
In this activity, you will examine the amino acid sequence of Cytochrome-C proteins from twenty
different species and compare that to a cladogram made using shared characters. Remember that
evolution, on a genetic level, is a change in the frequency of alleles in a population over a period of time.
Learning Goals:
1. Students observe the impact of different sequences of amino acids on speciation of organisms.
2. Students observe the overlap between biochemical and morphological (anatomical) similarities
and differences between species.
Materials:
 1 data sheet of amino acid sequences in Cytochrome-C proteins from 20 different species
Procedure:
1. Find the human, rhesus monkey, kangaroo, snapping turtle, bullfrog, and tuna on the data sheet
provided and underline their names. You may write on the data sheet provided for the purposes of
this lab.
2. Compare the human amino acid sequence with each of these five animals by counting the number
of times an amino acid in that animal’s cytochrome c is different from the amino acid in that same
position of the human sequence. Create a data table with two columns; organism name and the
number of amino acid differences compared to human. Record the number of amino acid
differences between human and the following organisms: rhesus monkey, kangaroo, snapping
turtle, bullfrog, and tuna. (5 points)
3. The cladogram below shows the relationships of the selected animals based on their shared
anatomical characters. For example, out of seven key traits, all of these animals have a dorsal
nerve cord, but only humans, monkeys, and kangaroos have mammary glands. Make a chart (like
you did with the T. Rex lab) matching the shared traits with the species that have them using + or signs. (7 points)
4. In your lab book, draw the previous cladogram and then indicate the number of amino acid
differences between humans and each of the other species where the hexagons are located. (2
points)
Discussion Questions (Unless otherwise specified complete sentences are required!!!):
1. Does the molecular data from the amino acid sequence differences between humans and the other
organisms generally agree with the cladogram? (1 point)
2. Based on the molecular data, how does the “human-monkey” relationship compare to the “duckchicken” relationship (which shows a total of three amino acid differences when compared to each
other)? (1 point)
3. If the molecular data, the structural similarities, and the fossil record all support the same pattern
of relationships, can we be fairly confident that the pattern is accurate? Why or why not? (2 points
– 1 answer and 1 defense)
4. Chickens and turkeys are both birds and have the same sequence of amino acids in their
cytochrome-c protein. Explain how two species can have identical cytochrome-c and still be
different species. (3 points – excellent, standard, weak)
5. Write a short paragraph summarizing the important information that can be obtained when
viewing a cladogram. (3 points – excellent, standard, weak)
Adapted from: WGBH Educational Foundation and Clear Blue Sky Productions, Inc. Copyright 2001.