Contact: Noelle Cockett, (801) 797-3903, fanoelle@cc.usu.edu
Writer: Kurt Gutknecht, (801) 797-2189, kurtg@cc.usu.edu
Gene Marker Aids Livestock Production
Forget washboard abdomens and sleeker thighs. When it comes to livestock, the latest rage is bigger butts.
For more than a decade, animal scientists have been intrigued by an inherited trait in sheep that results in larger buttocks--and leaner, less expensive meat. Now, the discovery of a genetic marker for the trait should bring meatier hindquarters in sheep and other livestock a step closer to reality.
The marker is linked to a trait called callipyge (an appropriately descriptive Greek word for "beautiful buttocks").
Since the trait was discovered in a ram in 1983, the mode of inheritance has puzzled researchers. The trait vanished and reappeared at baffling intervals, seemingly defying the conventional laws of inheritance. Discovery of the marker showed why--the gene inherited from the female is able to "turn off" the gene that her lambs receive from the male. This type of inheritance has been discovered previously, but the marker lets researchers closely link events at the molecular level with the actual expression of a trait, the first time such a tool has been available.
"Usually, the parental origin of the chromosome doesn't matter. That's not true in this case. The parent definitely matters," says Noelle Cockett, molecular geneticist at Utah State University, who identified the marker and characterized the inheritance of callipyge in collaboration with Michel Georges, molecular geneticist at the University of Liege, Belgium. They published their findings in the July 12 issue of Science magazine.
The marker will be useful in seeking other examples of this type of inheritance in livestock and humans, aiding efforts to sift the genetic component of traits from other factors.
One immediate benefit of the marker is a blood test that lets producers devise breeding schemes so most lambs have heftier hindquarters. This requires crossing normal-appearing males with two copies of the mutation with females lacking the mutation. Previously, these animals could not be identified without extensive and expensive breeding trials.
The marker will also help determine whether the callipyge gene (or genes similar to it) occur in other species of livestock. If not, it may be possible to transfer the callipyge gene from sheep to these species.
The actual callipyge gene should be identified within a few years, Cockett and Georges say.
The potential gains in meat production from callipyge are tantalizing--as much as a 30 percent increase in lean mass in the hindquarters, and improved feed efficiency. Unlike double-muscling in cattle, which caused calving problems, the callipyge trait is expressed after birth and does not interfere with lambing. Callipyge increases the size of selected muscle fibers, not the number of muscle fibers.
One potential obstacle is the reduced tenderness of meat from callipyge lambs, a problem which scientists think can be corrected through genetic selection and meat-processing techniques.
"The meat packers I've contacted say they prefer callipyge lambs if the tenderness problem can be solved," says Sam Jackson, animal scientist at Texas Tech University, who was the first to study inheritance of the trait and who provided samples for the molecular study. He notes that callipyge affects only the tenderness of the loin, not of the legs and shoulder.
The ongoing research effort involves flocks of sheep at USU, Texas Tech University, and the U.S.D.A. Sheep Experiment Station, Dubois, Idaho.
The ability to track the callipyge gene will pinpoint the factors that affect growth, fat deposition, and meat tenderness, says Jerry Taylor, geneticist at Texas A & M University. "The callipyge gene clearly illustrates how animal breeders will benefit from the molecular dissection of production traits," Georges says.
Most genetic traits are inherited in Mendelian fashion, in which expression of a trait makes it possible to predict what proportion of their progeny will also express the trait.
In contrast, only lambs that inherit the callipyge gene from the ram and the normal gene from their mother express the trait. Lambs with any other combination of genes, including those with two copies of the callipyge gene, appear to be normal.
Cockett and Georges refer to this type of inheritance as polar overdominance.
The researchers refuse to speculate on possible implications of their research on muscle building or buttocks toning in humans.
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