Retroviruses help unravel the history of sheep
27 April 2009
Specialised wool production began in South-west Asia, while other findings imply some truth behind a tale in the Bible, say the international team of researchers, led by scientists from the University of Glasgow.
Sheep were first domesticated 11 000 years ago in South-west Asia before spreading to Europe and the rest of the world. Initially, they were first selected for their meat and eventually also for secondary products like wool.
The new study used a family of endogenous retroviruses as markers to deduce the genetic lineage of 133 breeds of domestic sheep from various locations around the world.
Endogenous retroviruses integrate their DNA into the genetic code of the host they infect, enabling scientists to detect the remnants of ancient infections caught by sheep and their ancestors.
By testing for the presence of a particular set of retroviruses, known as enJSRVs, and comparing their prevalence in each breed of sheep, the researchers were able to distinguish primitive breeds of sheep from more recently domesticated ones.
"We have demonstrated how endogenous retroviruses can be used as a new class of genetic markers to unravel the history of a domesticated species," said Professor Massimo Palmarini from the University of Glasgow, who led the study.
The results support the theory that breeding of sheep for wool and other secondary products began in South-west Asia, before spreading to Europe through secondary migrations.
Matching the retrovirus signatures with the location of the sheep, they gained insight into ancient migration routes. For example, Orkney sheep were found to be closely related to breeds in Scandinavia, while the Soay sheep of St Kilda, Scotland, have links to the Mediterranean Mouflon.
Intriguingly, they also found that the Jacob sheep of the British Isles is more similar to South-west Asian and African breeds than other British sheep. The breed is named after the Biblical story of Jacob who is said to have taken "every speckled and spotted sheep" as a wage from his father-in-law, Laban. The note in the book of Genesis is possibly the first recorded use of selective breeding.
Image: credit: Wellcome Library, London
References
Chessa B et al. Revealing the history of sheep domestication using retrovirus integrations. Science 2009;324(5926): 532-36