"Mitochondria are the cell's power plants and possess their own genes that are
    inherited through the maternal line. Scientists use this method because
    mitochondrial DNA is more accessible, easier to sequence, and all
    multi-cellular animals have mitochondria, whereas all animals do not share the
    same nuclear genes" 

    "Results of the study are published in the July 1, 2001 issue of the journal
    Mammalian Genome" 

    "In recent years, scientists have increasingly relied on using mitochondrial DNA
    to make comparisons among mammals and thereby link those that are related
    on the evolutionary tree. 

    But Killian said that mitochondrial DNA provides misleading results for a
    variety of reasons. Most importantly, it requires more human input to decide
    which information is fed to the computer, thereby raising the risk of human
    bias. In fact, when the data were given to three different laboratories for
    analysis, they generated three different family trees, Killian said. 

    Secondly, the "bootstrap value" – a measure of the relatedness of genes --
    which the computer assigns to the accuracy of its predictions has been quite
    low in mitochondrial studies on mammalian associations, hovering between 40
    percent and 60 percent. 

    In contrast, the Duke study generated 97 percent to 100 percent bootstrap
    support in its nuclear gene comparisons of animals representing all three
    mammalian groups. Mammals they studied included the platypus, echidna,
    opossum, wallaby, hedgehog, mouse, rat, rabbit, cow, pig, bat, tree shrew,
    colugo, ringtail lemur and humans. 

    Other researchers on the paper include former Duke Research Fellow
    Thomas R. Buckley and Niall Stewart and Barry L. Munday of the School of
    Aquaculture at the University of Tasmania, Australia. 

    The study was funded by grants from the National Institutes of Health,
    Department of Defense, Sumitomo Chemical Company Ltd. and AstraZeneca
    Pharmaceuticals Ltd. 


    Note: This story has been adapted from a news release issued by Duke University
    Medical Center for journalists and other members of the public. If you wish to quote
    from any part of this story, please credit Duke University Medical Center as the
    original source. You may also wish to include the following link in any citation: 
    http://www.sciencedaily.com/releases/2001/07/010706081043.htm


    Extracts from "Sciencedaily.com"

    Source: Duke University Medical Center (http://www.mc.duke.edu/)

    Date:
                       
    Posted 7/6/2001

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