*Mountains of new data are challenging old views*
The established view of the genome began to take shape in 1958, just 5
years after Francis Crick and James D. Watson worked out the structure
of DNA. In that year, Crick expounded what he called the "central
dogma" of molecular biology: DNA's genetic information flows strictly
one way, from a gene through a series of steps that ends in the
creation of a protein. That principle developed into a modern
orthodoxy, according to which a genome is a collection of discrete
genes located at specific spots along a strand of DNA. This old view
got the basics right: that genes encode proteins and that proteins do
the myriad work necessary to keep an organism alive.
Researchers slowly realized, however, that genes occupy only about 1.5
percent of the genome. The other 98.5 percent, dubbed "junk DNA," was
regarded as useless scraps left over from billions of years of random
genetic mutations. As geneticists' knowledge progressed, this basic
picture remained largely unquestioned. "At one time, people said, 'Why
even bother to sequence the whole genome? Why not just sequence the
[protein-coding part]?'" says Anindya Dutta, a geneticist at the
University of Virginia in Charlottesville.
Closer examination of the full human genome is now causing scientists
to return to some questions they thought they had settled. For one,
they're revisiting the very notion of what a gene is. Rather than
being distinct segments of code amid otherwise empty stretches of DNA
- like houses along a barren country road - single genes are proving
to be fragmented, intertwined with other genes, and scattered across
the whole genome.
Even more surprisingly, the junk DNA may not be junk after all. Most
of this supposedly useless DNA now appears to produce transcriptions
of its genetic code, boosting the raw information output of the genome
to about 62 times what genes alone would produce. If these active
nongene regions don't carry code for making proteins, just what does
their activity accomplish?
http://www.sciencenews.org/articles/20070908/bob9.asp
--
Rado
"The obvious is that which is never seen
until someone expresses it simply."
- Christian Morgenstern