Download Molecular Evidence of Evolution – Cytochrome-C

Molecular Evidence of Evolution – Cytochrome-C
Name ______________________________
Intro: Cytochrome-C, an enzyme found in virtually all organisms, is needed for the release of energy from
food. The amino acid sequences in this protein from several different organisms are compared in
the diagram that follows. The differences between these amino acid sequences can be used to
infer the relatedness of the organisms.
Procedure:
1. Find the human, rhesus monkey, kangaroo, snapping turtle, bullfrog, and tuna on the “Amino Acid
Sequences in Cytochrome-C Proteins from 20 Different Species” chart provided.
2. Compare the human amino acid sequence to each of these five animals by counting how many
amino acids in that animal’s cytochrome-c are different from those in the human protein. Record
the number of differences between humans and each species in the table below.
Number of differences between humans and other species in cytochrome-c protein
Rhesus monkey
Kangaroo
Snapping Turtle
Bullfrog
Tuna
Species
Amino Acid
Differences
3. A cladogram is a graphical means of showing the relatedness of species based upon shared
traits. The branching nature of the cladogram is reflective of the branching nature of evolution.
The point where two evolutionary lines meet represents the most recent ancestor that they share
in common. The cladogram below shows the relatedness of several animals based upon
anatomical similarities. For example, out of seven key traits, all of these animals have a dorsal
nerve cord. We can infer that these animals all share a distant common ancestor that also had a
dorsal nerve cord. Only humans, monkeys, and kangaroos have mammary glands. We can infer
that they alone share a common ancestor that also had mammary glands.
Cladogram of seven animal species
lamprey
tuna
bullfrog
turtle
kangaroo
monkey
Placenta
Mammary glands
Amnion (fluid-filled sac that surrounds developing fetus)
Paired legs
Paired appendages + spinal column
Dorsal nerve cord + notochord
human
4. Record the number of differences you measured between the different amino acid sequences of the
cytochrome-c protein in the cladogram below. Write your answers in the circles below each arrow.
lamprey
tuna
bullfrog
turtle
kangaroo
monkey
human
Analysis:
1. Does the data from the amino acid sequence generally agree with the anatomical data that was
used to construct the cladogram?
2. Do organisms with fewer shared anatomical traits also have more differences in their proteins?
3. Based on the molecular data, how does the “human/monkey” relationship compare to the
“duck/chicken” relationship? (Which shows more amino acid differences?) What conclusion can
we make about the ancestry of humans and monkeys compared to ducks and chickens?
4. Based upon cytochrome-c comparison, do penguins appear to be more closely related to ducks
or to the chicken and turkey, or do penguins seem equally unrelated to both species? Explain
your answer.
5. If the molecular data, the structural similarities, and the fossil evidence all support the same
pattern of relationships, can we be fairly confident that the pattern of this cladogram is accurate?
Why or why not?
6. Chickens and turkeys both have the same sequence of amino acids in their cytochrome-c protein,
yet they are obviously different species. Explain how two species can have identical sequences
and still be different species.
7. The last three species on the chart are fungi. Construct a cladogram of these fungal species that
shows their relatedness based upon differences in the cytochrome-c protein. Species should be
grouped together on the same branch of the cladogram if they have fewer differences and share
more similarities in the cytochrome-c sequence. Provide the data that supports your conclusion.