ncestors diverged from the rest early in the lineage--with more recently derived angiosperm species, as well as with plant species outside the angiosperms. They took the opportunity to examine the genomes of a number of plant species for which only a partial DNA sequence has been determined. The team uncovered evidence of whole-genome duplications by confining their study to duplicated genes. The challenge was to distinguish isolated duplications from whole-genome duplications after a period of time in which direct evidence for a genome-wide duplication may have disappeared.

Any duplicated gene gives rise to two "paralogs," which are each subject to random, independent mutation. Most mutations in a gene's DNA sequence cause a change in the corresponding gene product. But "synonymous" mutations in DNA do not lead to a change in gene product, so natural selection has little effect on them and they remain in the genome. Because such mutations accumulate through time, the frequency of synonymous mutations between paralogs "can be used as a proxy for the time following the duplication," explains dePamphilis. Even after obvious signs of a whole-genome duplication have been lost, statistical analysis can detect a group of paralogs with very similar frequencies of synonymous mutations, indicating that all of those paralogs arose simultaneously--the hallmark of a whole-genome duplication.

A paleopolyploidy event previously demonstrated by other investigators is associated with a burst of evolution in the economically important grass family. The new results from the Penn State paper confirm a previously-reported paleopolyploidy event in eudicots (a group that includes beans, tomatoes, sunflowers, roses, and apples) associated with their rapid divergence, and demonstrates the first evidence of a paleopolyploidy event associated with the ancient explosion of all angiosperms.

Mere guilt by association? "We can take it farther than just correlatio
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Contact: Barbara K. Kennedy
science@psu.edu
814-863-4682
Penn State
11-May-2006

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