Will alien life be based on DNA? It seems like a good hypothesis, but really, all that's needed is a molecule that can store and duplicate information. Maybe alien "DNA" will have four-letter codons rather than three, or a different coding strategy, or maybe it's based on a totally different "information molecule!" Let's assume for now that our exploratory starships have finally found a planet rich in DNA-based lifeforms, and we've been busy sampling their DNA. Our exobiologist team has brought back 6 samples from different alien species, and our job is to build a cladogram, or branching tree, to see how they are related. We're pretty certain this group is all one related "clade" without any extinct parent species, so all 6 species will appear as one "tree." We also have two guesses as to the shape of this tree:
Now, the first thing we do is to run these six species' DNA through our gene-sequencer and compare them. At the bottom of this page, you can see a table we made comparing the DNA match of each species to each other species. (We have made up fanciful names for each species). Your job is to... 1) pick which one of the tree diagrams is most accurate, 2) then drag names of the species (in the blue bar) to their correct position on the cladogram. When you have filled in the diagram, you'll see the right answer. You can hit reset at any time. The DNA match numbers look confusing at first, because they're all so similar. Use the following clues: 1. A child species will be more similar to its parent (figure 98% similar) than to its "sibling" (sister) species. We assume these species evolved in different directions, so a sibling will have about twice the difference. 2. The most dissimilar species will likely be at the top and bottom of the cladogram. 3. Figure about 2% change or genetic drift per species. (this is actually very high) 4. If one tree shape doesn't work out properly, try the other. Content on this page requires a newer version of Adobe Flash Player.
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Montana State University
Astrobiology Short Course : Build An Alien Cladogram
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Will alien life be based on DNA? It seems like a good hypothesis, but really, all that's needed...