Gina Kolata writes in the New York Times about the discovery that "the human genome is packed with at least 4
million on-off switches that tell our genes what to do and when. The
switches reside in bits of DNA that once were dismissed as "junk" but
turn out to play critical roles in controlling how cells, organs and
other tissues behave."
"As they delved into the "junk" — parts of
the DNA that are not actual genes containing instructions for proteins —
they discovered it is not junk. At least 80 percent of it is active and
needed.
The result is an annotated road map of much of this DNA,
noting what it is doing and how. It includes the system of switches
that, acting like dimmer switches for lights, control which genes are
used in a cell and when they are used, and determine, for instance,
whether a cell becomes a liver cell or a neuron."
"The findings have applications for
understanding how alterations in the non-gene parts of DNA contribute to
disease, which might lead to new drugs.
They can also help
explain how the environment can affect disease risk. In the case of
identical twins, small changes in environmental exposure can slightly
alter gene switches, with the result that one twin gets a disease and
the other does not."
"In one of the Nature papers, researchers
link the gene switches to a range of human diseases — multiple
sclerosis, lupus, rheumatoid arthritis, Crohn's disease, celiac disease —
and even to traits like height.
In large studies over the past
decade, scientists found that minor changes in human DNA sequences
increase the risk that a person will get those diseases. But those
changes were in the junk, now often referred to as the dark matter —
they were not changes in genes — and it was not clear what their
significance was. The new analysis reveals that a great many of those
changes alter gene switches and are highly significant.
"Most of
the changes that affect disease don't lie in the genes themselves; they
lie in the switches," said Michael Snyder, a Stanford University
researcher for the project, called ENCODE, for Encyclopedia of DNA
Elements."
"Why would you need to have a million switches to control 21,000 genes?"
There also is a sort of DNA wiring system that is almost inconceivably intricate."
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