Mysterious Mammalian DNA Survives for Eons
Science | Thu, Oct 9, 2008 at 6:05:39 pm PDT
A fascinating discovery by scientists investigating the mammalian genome: Mysterious DNA Found to Survive Eons of Evolution.
Scientists have discovered mystery snippets of mammal DNA that have survived eons of evolution and yet have no apparent purpose. The finding reveals just how much we don’t know about the secrets hidden in our genome and that of other animals.
Most genes change throughout evolution via mutations; useless ones eventually get weeded out of the population while the helpful modifications take hold. However, about 500 regions of our DNA - the body’s instruction code made up of base pairs of molecules - have apparently remained intact throughout the history of mammalian evolution, or the past 80 million to 100 million years, basically free of mutations.
“Mutations are introduced into these regions just as they are everywhere else, but they’re swept out of the genome much more quickly,” said researcher Gill Bejerano, professor of developmental biology and computer science at Stanford University. “These regions seem to be under intense purifying selection - no mutations take hold permanently.”
And what’s more, many of those sequences do not appear to code for any obvious function, or phenotype, in the body. Researchers suspect they do serve an important purpose, but have yet to figure out exactly what that purpose is. (These sequences are not the same as non-coding or “junk” DNA, for which no function has been identified. Also, most junk DNA has not been conserved for eons like these segments.)
Ultraconserved regions
The researchers call these mystery snippets “ultraconserved regions,” and found that they are about 300 times less likely than other regions of the genome to be lost during the course of mammalian evolution. Bejerano and his graduate student Cory McLean detailed the finding in the Oct. 2 issue of the journal Genome Research.
The fact that these segments haven’t been weeded out by natural selection implies that they serve an important function in mammals. Yet mice in the lab bred to lack these DNA strands appear healthy and don’t seem to be missing any vital genes.
Wondering if the odd results were simply some fault of the lab experiment, and perhaps the mice really weren’t as well off as they seemed, the researchers investigated whether any other mammals were also blithely living without these regions.
Amazingly, they found that was not the case.
