Digital Biology Friday: Hey, who moved my DNA?

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Sandra Porter
Last week, we decided to compare a human mitochondrial DNA sequence with the mitochondrial sequences of our cousins, the apes, and find out how similar these sequences really are. The answer is: really, really, similar. And you can see that, in the BLAST graph, below the fold. A quick glance shows that the ape with the most similar mitochondrial sequence is Pan paniscus, the pigmy chimpanzee. Next, is Pan troglodytes, the chimp that we see in movies, and last we have Gorilla gorilla. Then we have a really curious, and unexpected, matching sequence. i-02d87f217a26438e8407078f3198ac5d-small_mito.gif Click the picture to see a larger image. This other sequence matches almost the entire length of the human mitochondrial genome. But it isn't in the mitochondria. It's located on human chromosome 17. This is even more intriguing (to me anyway) than our relationship with apes. How did a copy of the mitochondrial genome get out of the mitochondria, and into the nucleus, and get integrated into chromosome 17?i-1ebf120494a28b0ae8bc5204bac865b7-cell.gif Retroviruses? Something odd happening during meiosis? (Meiosis is the process of cell division, leading to the formation of the cells that go on, later, to become eggs or sperm). Like many discoveries, this one only leads to further questions:
When did this happen? Have mitochondrial genomes been inserted in the chromosomes of other animals? what about plants? or fungi? Are these genes expressed? That is, do they get transcribed and translated? We use mitochondrial DNA for identification purposes. Does having this extra sequence around cause any problems with identification? And what about all those kids, sending their mitochondrial DNA off to the Dolan DNA Learning Center to get sequenced? Which mitochondrial sequences are getting sequenced? Oh yeah, and the people who are getting their mitochondria sequenced from genetic testing companies, which sequences are they sequencing?
There would be more copies of a mitochondrial genome, in a cell, from mitochondria, than from the two copies we have of chromosome 17, that we inherited from our mom and dad. But, still.... It seems to me that the chance of mixing something up is pretty good. Ahem, weren't we going to learn how closely related we are to our hairy cousins? Oh yeah. Well, I'm easily distracted and way too short on time. Come back next week when we monkey around a bit with our BLAST results and, try again to see what we can learn about relatives. (or maybe look into this nuclear copy of the mitochondrial genome, just a bit further, who knows?) If you can't wait, you can get some of the answers in the tutorial section of Geospiza Education and look for the tutorial on Mitochondria and Chloroplasts as models for genomics. Read ahead: comparing apes and humans, building a tree

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