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The Callipyge Phenomenon: Evidence for Unusual Genetic Inheritance¹

N. E. Cockett^*,2, S. P. Jackson, G. D. Snowder, T. L. Shay^*, S. Berghmans, J. E. Beever^||, C. Carpenter^# and M. Georges

^* Department of Animal, Dairy and Veterinary Sciences, Utah State University, Logan 84322-4700 and Department of Animal Science and Food Technology, Texas Tech University, Lubbock 79409 and USDA, ARS, U.S. Sheep Experiment Station, Dubois, ID 84323 and Department of Genetics, University of Liége, 4000 Liége, Belgium and ^|| Department of Animal Sciences, University of Illinois, Urbana 61801 and ^# Department of Nutrition and Food Sciences, Utah State University, Logan 84322-8700

² To whom correspondence should be addressed (phone: 435/797-3903; fax: 435/797-3904; E-mail: fanoelle{at}cc.usu.edu).

Abstract

In 1983, a male lamb exhibiting a pronounced muscular hypertrophy, particularly noticeable in the hind quarters, was born into a commercial Dorset flock in Oklahoma. The ram was premonitorily called Solid Gold. He subsequently produced offspring expressing the unusual phenotype, which is referred to as callipyge (Greek: calli- beautiful + -pyge buttocks). Animals demonstrating the callipyge phenotype are all descendants of this founder ram. These animals produce leaner, higher yielding carcasses, but there is some concern with decreased tenderness of the loin. Genetic characterization of the locus has demonstrated a unique mode of inheritance termed polar overdominance, in which only heterozygous offspring inheriting the mutation from their sire express the phenotype. The three other genotypes are normal in appearance. Progeny data indicate that reactivation of the maternal callipyge allele occurs after passage through the male germ line, although this reactivation is not absolute. The callipyge gene has been mapped to the distal end of ovine chromosome 18.

¹ The authors thank Dave Forrester and Cole Evans for management of the Utah State University callipyge flocks. This project has received funding from the Utah Agricultural Exp. Sta., the Utah Centers of Excellence Program, and the USDA/NRI Competitive Grants Program (Grants #94-04358, #96-35205, and #98-03455). Approved as UAES journal paper no. 7080.