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Wednesday, November 2, 2011

Junk DNA separates human from chimp

Researchers from the Georgia Institute of Technology have found that large DNA insertions near but not within genes may account for the evolutionary differences between humans and chimpanzees.   This may answer the question of how the two species can be so dissimilar, despite having genes that are over 98% identical. 

While it is true that the coding regions (parts of the genome that code for amino acids) of chimps and humans are virtually identical, the regions around those genes are much less similar. You may know these locations outside genes as 'junk DNA'.  However, not all junk is created equal, and some of these sequences do have a function.  

For example, self-replicating genetic fragments called transposable elements have inserted themselves into the non-coding regions of both humans and chimps, sometimes in tens of thousands of copies. Although these insertions don’t alter the genes themselves, they can affect gene expression.  In other words, they can affect how many copies of a protein are made from a particular gene.  To give a couple of overly simplified examples, suppose that one protein is involved in intelligence, and another in production of body hair.  Chimps and people may have identical genes encoding those proteins, but they don’t make the same amounts of them.

As expected, the scientists found that variation between chimps and humans caused by large insertions in non-coding regions did affect gene expression.  This means, of course, that regulatory sequences may be as important as genes in driving evolution.

Illustration by Kayla Orlinsky, 10/27/2011.