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The callipyge (CLPG) phenotype is an inherited skeletal muscle hypertrophy described in sheep. It is characterized by an unusual mode of inheritance ("polar overdominance") in which only heterozygous individuals having received the CLPG mutation from their father (+^MAT/CLPG^PAT) express the phenotype [1]. +^MAT/CLPG^PAT individuals are born normal and develop the muscular hypertrophy at approximately 1 month of age. The CLPG mutation was identified as an A to G transition in a highly conserved dodecamer motif located between the imprinted DLK1 and GTL2 genes [2, 3]. This motif is thought to be part of a long-range control element (LRCE) because the CLPG mutation was shown, in postnatal skeletal muscle, to enhance the transcript levels of the DLK1, PEG11, GTL2, and MEG8 genes in cis without altering their imprinting status [4]. As a result, the +^MAT/CLPG^PAT individuals have a unique …