The "double-muscling" trait observed in the Piedmontese breed of cattle is due to a natural variation in the myostatin gene. Myostatin, also called GDF8, controls the growth of skeletal muscle. DNA testing identifies whether animals have zero, one or two copies of the Piedmontese double-muscling variant of the myostatin gene.

Animals can inherit the double-muscling gene type from just one parent (single copy) or both parents (double copy). Piedmontese double-muscling is dominant. This means that animals will show double-muscling if they have only a single copy. The only difference between single and double-copy animals is that a double copy will "breed true"—all their offspring will have the double-muscling trait. A single-copy animal can have offspring without the double-muscling trait (about half the offspring if mated to noncarrier animals).

The Piedmontese double-muscling variant is due to a single alteration in DNA sequence, from a guanine (G) in normal cattle to adenine (A) in Piedmontese, at position number 938 of the myostatin coding region. The DNA test distinguishes animals that are AA, AG or GG at this position. For more scientific information see the publication by McPherron and Lee "Double muscling in cattle due to mutations in the myostatin gene", Proceedings of the National Academy of Science USA Vol. 94, pp 12457-12461. 1997.

Test Results

Double copy, also called homozygote or AA genotype

  • This is where the Genotype is AA; the animal has the Piedmontese double-muscling gene variant only. These animals are called a "homozygote" or "double copy." Both the mother and the father of the animal passed on the Piedmontese double-muscling gene. This type of animal will always pass a copy of the Piedmontese double-muscling gene on to its offspring. We expect all offspring will have the double-muscling trait.

Single copy, also called heterozygote or AG genotype


  • Where the Genotype is AG, the animal has one copy of the Piedmontese double-muscling gene and one copy of the "normal" gene (found in other types of cattle). These animals are called a "heterozygote" or "single copy." This type of animal will only pass the Piedmontese double-muscling gene to some of its offspring (about 50%).

Noncarrier


  • Where the Genotype is GG, the animal does not contain the Piedmontese double-muscling gene. These animals are also called "noncarrier."