A technique used to determine evolutionary relationships is to study the biochemical similarity of
organisms. Though molds, pigeons, and humans appear to have little in common physically, a study of their
proteins reveals certain similarities. Biologists have perfected techniques for determining the sequence of
amino acids in proteins. By comparing the amino acid sequences in homologous proteins of similar
organisms and of diverse organisms, evolutionary relationships that might otherwise go undetected can be
determined. The greater the similarity between the amino acid sequences of two organisms, the closer their
relationship. Conversely, the greater the differences, the more distant the relationship.
1. Figure 1 compares corresponding portions of hemoglobin molecules in humans and five other vertebrate
animals. Hemoglobin, a protein composed of several long chains of amino acids, is the oxygen-carrying
molecule in red blood cells. The sequence shown is only a portion of a chain made up of 146 amino acids.
The numbers in Figure 1 indicate the position of a particular amino acid in the chain.
2. In Data Table 1, notice that the abbreviated names of the amino acids in human hemoglobin are printed
for you (for comparison).
3. In the appropriate spaces in Data Table 1, write the abbreviated name of each amino acid in chimpanzee
hemoglobin that is DIFFERENT from that in human hemoglobin. If there are no differences, leave the
4. For the remaining organisms, write the abbreviated names of the amino acids that do not correspond to
those in human hemoglobin. Note: Always be sure that you compare the amino acid sequence of each
organism with that of the human and not the organism on the line above.