www.whyville.net Nov 16, 2008 Weekly Issue

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Cancer Genome Sequenced

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(November 6) A really cool finding was published in the journal "Nature" today! Scientists at Washington University in St. Louis reported that they have sequenced the entire DNA genome of a patient with acute myeloid leukemia, which gives them exciting new information about how her cancer was caused.

OK, let's back up for a minute. We've talked before about genomes, and how they are the total of the entire DNA in one person (or other organism). At the time that each of us were first created, all the cells in our body had the exact same genome. So in theory, all of our body cells, which are all copies or modified versions of those very first cells, should all have the same genome, too. But scientists have known for a long time that it doesn't quite work that way. Over time, as the genome is replicated, or copied, to make new cells, sometimes there are changes in the DNA, called mutations. This actually happens all the time, for a number of reasons - mistakes made by proteins in the cell, or damage from outside forces like chemicals and UV light. But the cell has a number of mechanisms to repair almost all of the errors right away, so that generally a lasting mistake occur about 1 in 1,000,000,000 nucleotides of DNA.

Many mistakes are silent, meaning they don't cause any trouble at all, but many other mutations lead to a variety of diseases. Cancer can occur when certain mutations aren?t corrected, causing mutated cells to multiply and grow into tumors. Because the cells in the tumors all came from an original mutated cell, the tumor genome will be different from the normal genome of the cancer patient (the genome from her eye cells, for example).

In this new research, scientists determined the entire sequences of both the normal genome and the leukemia cell genome and compared the two. By studying the differences between the genomes, scientists saw, for the very first time, all of the mutations that were present specifically in the cancer cells, but not in normal cells. This provides new information about the types of DNA changes that contribute to cancer. It's important to note that cancer is caused by a number of things all going wrong, not just one mutation here or there. So these new findings provided a big-picture view of all the things that went wrong in the patient's cells, but there is still work to be done on understanding which mutations actually helped cause the cancer. This is a very big first step in figuring all that out.

This issue of Nature has a number of great articles about this topic. Would you ever want your genome sequenced? What kind of information would you want to find out? I totally want to do it, mostly to see just how identical my twin sister Jhilya and I are, 30 years after the embryo divided. That's a long time to accumulate mutations; I'd be curious what our genomes look like! (Sis, are you reading? Wanna get sequenced?)

Author's Note: Sources:

Editor's Note: For more blogs from Dr. Rabiah, visit Science Chicago's website at: http://www.sciencechicagoblog.com


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