Gene found for big, firm sheep rumps

Scientists have found the gene that gives some sheep unusually big, muscular bottoms.

GENE EFFECT. A gene called callipyge can give a sheep a bigger and more muscular rump (left) than usual (right). Duke University Medical Center

Sheep bearing one gene variant, dubbed callipyge (from the Greek for shapely buttocks), convert food into muscle 30 percent more efficiently than usual, report scientists at the Agricultural Research Service in Clay Center, Neb., and at Duke University in Durham, N.C. The gene may inspire insights into fat metabolism and muscle formation, he says.

For a decade, scientists have been searching for a genetic explanation of the unusually meaty posteriors of certain sheep. The newly found gene was elusive. Although a copy is inherited from each parent, only the dad’s version ends up being active. Moreover, the sheep only develops the characteristic big rump when the dad contributes the special gene version and the mom provides the common form.

To find the gene, Brad Freking of the Agricultural Research Service and his colleagues compared stretches of DNA from inbred big-bottomed sheep with the same genetic stretch from regular sheep. Some 600 differences showed up between the two, but only one correlated with differences in bottom size. The researchers report their findings in the October Genome Research.


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Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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