This is one of 30 lessons from the NSTA Press book Scientific Argumentation in Biology. The lesson engages students in an argumentation cycle in which they use evidence from their analysis of the amino acid sequences 1-40 for the hemoglobin subunit alpha protein for nine mammals (elk, caribou, cow, pallid bat, big-eared bat, golden hamster, mouse, musk shrew, and nine banded armadillo) to make an argument for which of these mammals are the most closely related. Students create a cladogram that shows the branching of lineages of the nine mammals. As they construct their argument, students build and apply knowledge of modern phylogenetics, which classifies organisms based on evolutionary history. The lesson includes an introductory reading on Darwin’s idea of descent with modification, an example of homologous structures in vertebrate limbs, and instructions on how to create a cladogram. Subsequently, students are asked to examine the relatedness of the 9 mammals, constructing their own cladogram, based on the amino acid sequence 1-40 for the hemoglobin subunit alpha protein. Students strengthen their understanding that common ancestry and biological evolution are supported by multiple lines of empirical evidence by reading about homologous structures in vertebrate limbs and using the amino acid sequences as evidence to make their argument for relatedness. Teachers are encouraged to refer to the preface, introduction, student assessment samples, and appendix provided in the full book for important background on the practice of argumentation and resources for classroom implementation.
Educator and learner
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