Report: Not all evolution has purpose

BALTIMORE (Map, News) - Repetitive DNA sequences that make up more than 40 percent of our genome rose to prominence without offering any benefits to the human race, researchers at Johns Hopkins University reported.

“For a long time, the basic belief of evolution was that all random genetic changes that manage to stick around have some selective advantage,” Nicholas Katsanis, associate professor at Johns Hopkins’ Institute of Genetic Medicine said in a statement. “But our work adds to the case that frequently, we are what we are largely due to random changes that are completely neutral.”

Describing their contributions to genetic drift online in Public Library of Science Genetics, Katsanis says the Johns Hopkins experiments demonstrated that many sequences do not produce any useful proteins for cell function.

Studying the whole human genome, they found more than 1,200 such pieces of mitochondrial DNA of various lengths embedded into regular DNA chromosomes. The mitochondria — the powerhouse of the cell — has its own, independent genome, passed down only from the mother. While chimps have a comparable number, mice and rats only have about 600 sequences. Since they increase in frequency as species advance, it suggested there was some evolutionary purpose to keeping them around.

Strikingly, however, none of these sequences contained the blueprint (an actual gene) to make a protein that does anything, nor did they seem to control the function of any nearby genes, said Katsanis. “If anything, they may be mildly negative since long repeat sequences can be unstable or get inserted inside genes and disrupt them.”

khille@baltimoreexaminer.com

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