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.