Callipyge gene in sheep

Double muscled sheep


  • The gene was found as early as 1980's

  • Comes from Greek known as 'beautiful buttocks'

  • Solid Gold was a ram born 20 years ago was the first born with callipyge gene

  • Known for having tough meat and using their resources for muscle

What is Callipyge gene or "beautiful buttocks'

It is a gene that can be passed on from either parent but is only expressed if the sire passes it on to his offspring. The gene is known for causing the lamb to putting all of its resources into making muscle. It causes a 30% increase in lean meat in the hindquarters. Unlike the double muscling gene in cattle, this gene is expressed after birth. It increases the size of selected muscle fibers however, it does not increase the number of muscle fibers.
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Genetic Transmission

  • CLPG phenotype is a single gene that is dominant when inherited from the sire.
  • The occurrence of this phenotype is 50% when a heterozygous male is mated to a population of normal, noncarrier females.
  • Mating heterozygous carrier females to normal noncarrier males results in 100% normal phenotype.
  • When lambs from the latter matings are phenotyped, 50% carry the CLPG gene, which results in 50% CLPG expression in lambs produced from these males when mated to normal noncarrier females.
  • This unique inheritance pattern has been termed "polar" overdominance.


Sheep are only callipygous if their father is; mutant mothers do not pass the trait on.

Two big-bottomed sheep will have snake-hipped offspring. How the two mutants cancel each other out is still a mystery.

Callipyge Sheep Presentation

Implications of allowing the breed to proliferate within the Southdown breed

1. Discrimination against Southdowns as a breed regarding marketability to the consumer

2. Discrimination against Southdowns for those who do not want the gene in their flocks.

3. Disqualification of Southdowns at stock shows that exhibit the gene.

4. Fraudulent representation of these animals by some breeders as normal, well- muscled sheep... duping uneducated buyers into purchasing a Callipyge carrier.

5. Increased disputes between buyer and seller from the sale of animals carrying the gene.

6. Promotion of a gene that could have a negative industry-wide implications

7. Potential for more difficulty during lambing.

8. Increased cost for genetic testing for the gene

9. Extreme difficulty in eliminating the gene for your herd once it has been introduced due to irregular inheritance pattern and lack of a commercial test.

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Spread of the Callipyge gene

Solid Gold was bred extensively he was the only known carrier at the time. His offspring were spread all throughout the country. Years later research was conducted involving his descendants, determining that the excessive muscling was due to a mutated gene named "Callipyge gene." It was then found that the gene has unique inheritance patterns, however, if the gene receives two copies the gene will not express itself.
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Red flags that may indicate that the gene may be present in an individual

1. Extreme, well-defined muscling of the leg muscles, forearm, loin and rack.

2. Tendency to have a steep hip

3. Be wary of flocks that tend to have some lambs that are extreme in their muscle design with the other sheep in the same flock having average to below average amounts of muscle mass.

4. These sheep tend to be marketed in the wool and when they are less than 90 days old in order to mask some of the more extreme aspects of their muscle mass.

5. If you view a lamb and the muscle mass appears almost too much to be true, then be very suspicious that the lamb may be carrying the gene.

Diagnosis and control/ eradication of gene

There are not many ways of testing for the gene besides DNA or blood testing. Both of which are not cost effective to any livestock production farm. Since the gene is passed on randomly there is no known way of eradicating the gene.


Would it be ethical to cull the sires that express the gene and the carriers since it is not a life-threatening disease? What would be the most cost effective of way of dealing with the disease?


This gene is "polar" overdominance and has baffling inheritance patterns. One method of testing for the gene is blood testing. Since the trait has a 50% chance of showing up in a lamb that had the dam or sire testing positive for it. The gene was only expressed if the sire passed it on while the lamb that the gene passed on through the dam was only a carrier of it. The meat is known to be tougher and leaner than sheep who do not express the gene. Since sheep producers are trying to produce a quality product having the gene present is counter productive.

References (Literature)

American Sothdown Breeders Association. "News." American Southdown Breeders Association. American Southdown Breeders Association, 27 Apr. 2015. Web. 29 Apr. 2016. <>.

Gutknecht, Kurt, and Noelle Cockett. "Gene Marker Aids Livestock Production." EurekAlert! Utah State University, 12 July 1996. Web. 29 Apr. 2016.

Jackson, S.P., and J.R. Blanton, JR. "Review: The Callipyge Gene in Sheep." Professional Animal Scientist, n.d. Web. 29 Apr. 2016. <>.

Jirtle, Randy L. "Geneimprint." : Press : 'Beautiful Buttocks' Pinned Down. Geneimprint, 15 Sept. 2002. Web. 29 Apr. 2016. <>.

Whitfield, John. "Mutation Gives Sheep Beautiful Buttocks." Nature Publishing Group, 17 Sept. 2002. Web. 29 Apr. 2016. <>.

Winstead, Edward R. "Genetic Mutation Explains ‘beautiful Buttocks’ in Sheep." Genetic Mutation Explains ‘beautiful Buttocks’ in Sheep. Genome News Network, 25 Oct. 2002. Web. 29 Apr. 2016. <>