Biology Lab Activity
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Amino Acid Sequences and Evolutionary Relationships
Introduction:
A technique used to determine evolutionary relationships is to examine the biochemical similarity among
organisms. Though mold, aardvarks, and humans appear to have little in common physically, a study of
their DNA and proteins displays many similarities. By comparing the amino acid sequence in similar
proteins of similar organisms and of diverse organisms, evolutionary relationships that may have
otherwise been undetected may be determined. Biologists believe that the greater the similarity between
two organisms’ DNA and amino acid sequences, the closer their relationship. Also the greater the
differences are, the more distant the relationship is. This is because if the relationship is distant, there
has been more time since the divergence of those two organisms for mutations to accumulate. Scientists
have found that such biochemical evidence compares favorably with other lines of evidence for
evolutionary relationships. In this activity, you will compare amino acid sequences in proteins of several
different organisms and infer evolutionary relationships among them.
Procedure:
1. Examine table 1. It compares corresponding portions of the protein, hemoglobin, in humans and five
different animals. Hemoglobin is the protein found in the red blood cells of mammals that transports
oxygen. The sequence of amino acids shown in figure 1 is only a portion of the chain of 146 amino acids
that makes up a subunit of the hemoglobin protein. The numbers in figure 1 indicate the position of a
particular amino acid in the chain.
2. In table 1, underline or highlight any amino acid in the animal’s sequence that is different from
humans. Always be sure you are comparing the amino acid sequence of the organisms with that of the
human and not the organism on the line above.
Table 1: Hemoglobin’s Amino Acid Sequence in Different Species
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Based on an activity in the 1995 edition of the laboratory manual for Biology by Miller and Levine.
3. Record the total number of differences in amino acids between humans and different organisms in the
table below.
Organisms
Number of Amino Acid Differences
Human and Chimpanzee
Human and Gorilla
Human and Rhesus Monkey
Human and Horse
Human and Kangaroo
4. In the space below construct a bar graph or histogram that shows the number of amino acid
differences between humans and the different kinds of animals.
Questions: Use complete sentences!
1. On the basis of hemoglobin similarity, which organism appears to be most closely related to humans?
Explain your answer.
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Based on an activity in the 1995 edition of the laboratory manual for Biology by Miller and Levine.
2. On the basis of hemoglobin similarity, which organism appears to be most distantly (least closely)
related to humans? Explain your answer.
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3. There is a difference of only one amino acid in the chain of hemoglobin of humans and gorillas. What
might have caused this difference in amino acid sequence?
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4. If amino acids sequences in the proteins of two organisms are similar, why will their DNA also be
similar?
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5. Many biologists believe that the number of differences between the proteins of different species
indicates how long ago the species diverged from a common ancestor. Why do these biologists believe
that humans, chimpanzees, and gorillas diverged from a common ancestor only a few million years ago,
which is not very long in evolutionary history?
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Based on an activity in the 1995 edition of the laboratory manual for Biology by Miller and Levine.