 The
saying “one person’s junk is another person’s
treasure” may apply to more than our possessions. A UCSD study
has found that genetic material derisively called “junk” DNA—because
it does not contain the instructions for protein-coding genes and
appears to have little or no function—is critically important
to an organism’s evolutionary survival.
Peter Andolfatto, an assistant professor of biology, reported in
the journal Nature that these non-coding regions play an important
role in maintaining an organism’s genetic integrity. In his
study of the genes from the fruit fly Drosophila melanogaster, he
discovered that these regions are strongly affected by natural selection,
the evolutionary process that preferentially leads to the survival
of organisms and genes best adapted to the environment.
Andolfatto’s findings are important because the similarity
of genome sequences in fruit flies, worms and humans suggest that
similar processes are probably responsible for the differences between
humans and their close evolutionary relatives. “Sequencing of the complete genome in humans, fruit flies, nematodes
and plants has revealed that the number
of protein-coding genes is much more similar among these species
than expected,” he says. “Curiously, the largest difference
between major species groups appears to
be the amount of ‘junk’ DNA rather than the number of
genes.”
Andolfatto showed that these expansive regions of “junk” DNA,
which in Drosophila account for about 80 percent of the fly’s
total genome, are evolving more slowly than expected. “This
pattern most likely reflects resistance to the incorporation of new
mutations,” he notes. “In fact, 40 to 70 percent of new
mutations that arise in non-coding DNA fail to be incorporated by
this species, which suggests
that these non-protein-coding regions are not ‘junk,’ but
are somehow functionally important to the organism.”
He also found that “junk” regions exhibit an unusually
large amount of functional genetic divergence between different species
of Drosophila, further evidence of their importance to organisms.
This implies that, like evolutionary changes to proteins, changes
to these “junk” parts of the genome also play an important
role in the evolution of new species. 
— Kim McDonald
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