[Paleopsych] UCSD Study Shows 'Junk' DNA Has Evolutionary Importance

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UCSD Study Shows 'Junk' DNA Has Evolutionary Importance
http://ucsdnews.ucsd.edu/newsrel/science/mcjunk.asp
    October 19, 2005

    By Kim McDonald
    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 actually critically important to an
    organism's evolutionary survival, according to a study conducted by a
    biologist at UCSD.

    In the October 20 issue of Nature, Peter Andolfatto, an assistant
    professor of biology at UCSD, shows 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 differences between major species groups
    appear to be the amount of `junk' DNA rather than the number of
    genes."

    Using a recently developed population genetic approach, Andolfatto
    showed in his study that these expansive regions of "junk" DNA--which
    in Drosophila accounts for about 80 percent of the fly's total
    genome--are evolving more slowly than expected due to natural
    selection pressures on the non-protein-coding DNA to remain the same
    over time.

    "This pattern most likely reflects resistance to the incorporation of
    new mutations," he says. "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."

    Andolfatto also found that "junk" regions exhibit an unusually large
    amount of functional genetic divergence between different species of
    Drosophila, further evidence that these regions are evolutionarily
    important 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.

    "Protein evolution has traditionally been emphasized as a key facet of
    genome evolution and the evolution of new species," says Andolfatto.
    "The degree of protein sequence similarity between humans and
    chimpanzees, and other closely-related but morphologically distinct
    taxa, has prompted several researchers to speculate that most adaptive
    differences between taxa are due to changes in gene regulation and not
    protein evolution. My results lend support to this view by
    demonstrating that regulatory changes have been of great importance in
    the evolution of new Drosophila species."

    Comment: [6]Peter Andolfatto (858) 334-8039

    Media Contact: [7]Kim McDonald (858) 534-7572

References

    2. http://www-er.ucsd.edu/
    3. http://ucsdnews.ucsd.edu/
    4. http://ucsdnews.ucsd.edu/releases
    5. http://ucsdnews.ucsd.edu/graphics/images/2004/fruitfly_lg.jpg
    6. mailto:pandolfatto at ucsd.edu
    7. mailto:kmcdonald at ucsd.edu