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Walruses and whales are both marine mammals. So are dolphins, seals, and manatees. They all have streamlined bodies, legs reduced to flippers, blubber under the skin and other adaptations for survival in the water. Although mammals evolved on land, these species have returned to the sea. Did they evolve from a single ancestor who returned to the ocean, or were there different return events and parallel evolution? We can't go back in time to observe what happened, but DNA sequences contain evidence about the relationships of living creatures. From these relationships, we can learn about the evolutionary history of marine mammals.
In this lab, students use sequence information in GenBank (the public repository of all known DNA and protein sequences from many species) and bioinformatics software to test hypotheses about the relationship between aquatic mammals (seals, whales, dolphins, walruses, manatees, and sea otters) and their potential ancestral relationship to land mammals. In the process, students learn how to build cladograms from molecular data and how to analyze them to make phylogenetic conclusions.
This lab requires a computer lab. Optimally with the teacher's computer projected so that students can initially follow along. In addition, two software products must be installed on each computer ahead of time:
A sample lab report for this exercise is available to teachers in the Teachers Vault.