Digital Biology Friday: Monkeying around with mitochondrial DNA

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Sandra Porter
The past few Fridays, we've been comparing human mitochondrial DNA with the mitochondrial DNA of different apes. We started doing this here, where you can find directions for getting started. And, we've found some interesting things. In this installment, we found that humans have practically an entire mitochondrial genome stuck in chromosome 17. Last week, we found that human mitochondrial DNA is more similar to that of chimpanzees than to gorillas. We found that 90.6% of the bases in human mitochondrial DNA match bases in the Bonobo chimp and 90.7% match bases in the Chimpanzee. This week, we're going to compare all four species to each other. The first thing that I did was to do blastn searches with the other mitochondrial sequences. First, I compared the mitochondrial sequence from Pan paniscus to that of Pan troglodytes and the gorilla. Notice, the two chimps match along the whole length of the mitochondria, but the gorilla sequence shows some gaps where the bases don't match. i-d8d2a33d6e8b9c451bdd3e2cbd780953-pan_blast.gif Then I compared Pan troglodytes to the gorilla, and added up the matching bases across the length of the mitochondria for each comparison and determined the fraction that matched for each comparison. This gave me a matrix like this: i-55512198b140a384ab879b3507b67054-pan_table.gif That information was enough for me to draw a cladogram. Cladograms are graphs that show evolutionary relationships but they don't include information about time. For my cladogram, I put the two species together that were most closely related - Pan paniscus and Pan troglodytes. Then I added humans, and last gorillas. i-5a95ce9a7bdaf0e4688c4ae88ab696c6-ape_tree.gif Since I wanted a nicer picture, I also converted my matrix to a different file format and ran the neighbor joining program from Phylip (apparently there's a new version, 3.66, that just came out this month, but I doubt that would matter for this analysis). Then I used NJ plot to view the tree. There you have it, Pan paniscus and Pan troglodytes are the most closely related. For some reason I thought, ahead of time, that the mitochondrial DNA of chimps and gorillas would be more similar to each other than to humans, but I was wrong. Human and chimp mitochondrial DNA were both 87% similar to the mitochondrial DNA from gorillas. Come back for next Friday, for more monkeying around. Wink, wink, nudge, nudge.

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