Fwd: Genome's Riddle: Few Genes, Much Complexity

From: Wade T.Smith (wade_smith@harvard.edu)
Date: Tue Feb 13 2001 - 13:42:55 GMT

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Subject: Fwd: Genome's Riddle: Few Genes, Much Complexity
Date: Tue, 13 Feb 2001 08:42:55 -0500
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From: "Wade T.Smith" <wade_smith@harvard.edu>
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    There is, in today's NYTimes, yet another article about the genome- but
    I've only included what seemed to me especially interesting below- which
    is a mechanism involved in replication that, I think, might well describe
    mechanisms we have started to call memetic.

    - Wade

    ********************

    READING THE BOOK OF LIFE

    Genome's Riddle: Few Genes, Much Complexity

    By NICHOLAS WADE

    http://www.nytimes.com/2001/02/13/health/13HUMA.html?pagewanted=all

    <snip>

    Turning from genes to chromosomes, one of the most interesting
    discoveries in this week's papers concerns segmental duplications, or the
    copying of whole blocks of genes from one chromosome to the other. These
    block transfers are so extensive that they seem to have been a major
    evolutionary factor in the genome's present size and architecture. They
    may arise because of a protective mechanism in which the cell reinserts
    broken-off fragments of DNA back into the chromosomes.

    In Celera's genome article, Dr. Venter presents a table showing how often
    blocks of similar genes in the same order can be found throughout the
    genome. Chromosome 19 seems the biggest borrower, or maybe lender, with
    blocks of genes shared with 16 other chromosomes.

    Much the same set of large-scale block transfers seems to have occurred
    in the mouse genome, Dr. Venter writes, suggesting that the duplications
    "appear to predate the two species' divergence" about 100 million years
    ago. He hopes that by sequencing the genomes of many other species he can
    reconstruct the history of the genome's formation.

    Segmental duplication is an important source of innovation because the
    copied block of genes is free to develop new functions. An idea enshrined
    in many textbooks is that the whole genome of early animals has twice
    been duplicated to form the vertebrate lineage. There are several cases
    in which one gene is found in the roundworm or fly and four very similar
    genes in vertebrates. (The quadruplicated genes that failed to find a
    useful role would have been shed from the genome.)

    But neither Celera nor the consortium has found any evidence for the
    alleged quadruplication. If this venerable theory is incorrect, the
    four-gene families may all arise from segmental duplication.

    </snip>

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