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An advance in genomics, the ID of growth genes in oysters has relevance for
farming and aquaculture, February 2007.

How many genes influence a complex trait, like weight, height or body
type?

And why does the answer matter?

Among other reasons, because the "Green Revolution" that multiplied crop
yields has to be followed by a "Blue Revolution" in ocean farming, according
to marine biologists at the University of Southern California.

"We?re going to have to make future decisions as a society how to provide
enough food for a growing population," said Donal Manahan, co-author of a
study on oyster growth appearing online this week in Proceedings of the
National Academy of Sciences Early Edition.

Currently a delicacy, oysters fed the masses in the past and could again
become "the soy bean of the sea" as traditional fisheries collapse, Manahan
predicted.

He and senior author Dennis Hedgecock linked growth rate in oysters to
approximately 350 genes, or 1.5 percent of the more than 20,000 genes in the
oyster genome.

To the authors? knowledge, this is the first estimate of the number of genes
that determine growth rate in any animal.

Specifically, the authors discovered the genes responsible for "hybrid
vigor," or the ability of some children of crossbreeding to outgrow both
parents. Hybrid vigor is of evolutionary as well as agricultural interest
because it appears to favor biodiversity.

Many plants have hybrid vigor. Seed companies exploited this property to
increase corn yields seven-fold from the 1920s to the present.

Most animals do not express hybrid vigor to such an extent, the authors
said. That makes oysters particularly strong candidates for aquaculture.

"Their hybrids grow much faster than either of the parents. And this is
exactly like corn," Manahan said.

The PNAS study may lead to improved breeding both on land and sea. The green
revolution worked by trial and error, with companies trying every possible
cross of corn strains to find the best hybrids.

"A century after its discovery in corn, we still don?t know why plants have
hybrid vigor, despite the economic and evolutionary importance of this
phenomenon," Hedgecock explained.

Knowing the genes for hybrid vigor may enable companies to develop the best
cross of corn strains, or oyster types, without guesswork.

The lines would not be genetically modified, only screened and matched as in
a dating service.

The goal is efficient and sustainable domestication of oysters and other
promising ocean species, mostly shellfish. Oysters already are the number
one farmed aquatic species worldwide.

Aquaculture of large fish remains environmentally challenging, Manahan and
Hedgecock noted.

Another problem is the apparent lack of hybrid vigor in most fish. Even in
oysters, the researchers found the rules of hybrid vigor to be more
complicated than predicted by classical ideas in genetics and physiology.

For example, some genes were expressed much less in the offspring than in
either parent, a pattern the authors call "underdominance." Very few genes
were expressed as the average of the expression in their parents.

Hedgecock called the underdominance patterns "one of the more surprising
findings" of the study.

Other authors on the study were USC graduate student Eli Meyer and
biotechnology company Solexa Inc. researchers Ben Bowen, Christian
Haudenschild, Jing-Zhong Lin and Shannon DeCola.

The U.S. Department of Agriculture, the W. M. Keck Foundation and the
National Science Foundation funded the research.

[www.eurekalert.org]