Domesticated goats show unique gene mix
Bruce Bower
Science News
5-12-2001
Goats have long been a favorite of farmers for good reason. They can survive on seemingly inedible scraps of vegetation in the harshest environments. And they provide milk, meat, skin, and fibers without taking up much space.
After domestication of the Eurasian wild bezoar, shown here, transport and trading of goats may have fostered a high degree of genetic unity in these animals.
Those qualities go a long way toward explaining why domesticated goats in Europe, Africa, and Asia share a striking degree of genetic similarity, according to the scientists who discovered the pattern.
The surprising amount of genetic unity among far-flung goat populations reflects these versatile animals' popularity as portable trading items in ancient times, contend geneticist Gordon Luikart of Université Joseph Fourier in Grenoble, France, and his coworkers. That mobility, which extended across continents, prevented goats in different parts of the world from developing regional genetic signatures, Luikart says.
"Goats might have played an important role in historical human colonizations, migrations, and commerce," he and his coworkers propose in the May 8 Proceedings of the National Academy of Sciences.
Unlike goats, cattle and other domesticated animals were bred in various locations without much mixing of animals from separate geographic regions. Earlier analyses found that these creatures display different genetic patterns from one continent to another.
Luikart's team obtained blood samples from 406 goats representing 88 domesticated breeds and from 14 wild goats, each of a different species. The animals came from Europe, Africa, and Asia. For each blood sample, the scientists extracted mitochondrial DNA, genetic material that's passed exclusively from mothers to their offspring.
An analysis of differences in genetic sequence along a specific stretch of mitochondrial DNA revealed three goat groups that arose from genetically distinct populations. Today, their distributions overlap.
Those three populations, in turn, emerged from a common maternal ancestor that lived around 200,000 years ago, the researchers estimate.
To date goat domestication, the scientists next examined sequences in another stretch of mitochondrial DNA. For this analysis, they used the genetic material of two goats from each of the three genetic lineages.
Patterns of genetic diversity indicated that one lineage experienced marked population growth—a sign of domestication—about 10,000 years ago in the Middle East. Archaeologists have already proposed that goat domestication first occurred at that time in what is now western Iran (SN: 4/8/00, p. 235).
The other two genetic lineages expanded more recently, one in western Asia around 6,000 years ago and the other in southeastern Asia about 2,000 years ago.
Goats may indeed have been traded widely in the ancient world, say two Irish researchers in a commentary published with the new study. Goat genetic history will probably get revised further as scientists examine more mitochondrial samples and probe male lineages using the Y chromosome, say David E. MacHugh of University College and Daniel G. Bradley of Trinity College, both in Dublin.
"There should be plenty more surprises in store," MacHugh and Bradley conclude.