Two 50-minute class periods.
Students then take home the activity to complete the discussion questions and the graph.
Working in groups of two, students begin by determining the number of amino acid differences in beta hemoglobin that occur between each of the pairs of organisms featured in the activity. The students do not know the names of the organisms studied until after they complete the amino acid comparisons and have begun the discussion. Students compare each possible pairing of organisms, looking for differences in the sequences, and discovering patterns in the degree of difference. The current view is that the number of differences for a particular molecule is an indicator of how long ago in the past any two organisms may have shared a common ancestor. By example, the relatively few differences between the beta hemoglobin of humans and gorillas is an indicator of a relatively recent common ancestor, whereas, a comparison of chimpanzee and lemur beta hemoglobin indicates a far more distant common ancestor.