Download Molecular Cladogram

Molecular Cladogram
Cytochrome-C, an enzyme (protein) 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.
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
Species
Amino Acid
Differences
Rhesus monkey
Kangaroo
Snapping Turtle
Bullfrog
Tuna
You completed this cladogram below showing 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
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
1.
What is the pattern for the number of amino acid differences?
2.
Does the data from the amino acid sequence generally agree with the anatomical data pattern?
3.
If 2 organisms had fewer shared anatomical traits did they also have more differences in their proteins?
Please note this is an important question!
4.
Based on the molecular data, how does the “human/monkey” relationship compare to the “duck/chicken”
relationship? (Which shows more amino acid differences?) What does the evidence say about the ancestry
of humans and monkeys compared to ducks and chickens?
5.
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 using
evidence!
6.
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?
7.
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.
8.
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 cytochromec sequence. Use the evidence to support your claim.