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Science & Technology

China loses its patent

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Author(s): Tiasa Adhya
May 31, 2010 | From the print edition

Human’s best friend originated from a wolf in West Asia
 

The world’s heaviest and largest dog was a Saint Bernard. Named Benedictine, it measured nearly 275 cms in length and weighed 162 kgs. The world’s smallest breed of dog is named after the state of Chihuahua in Mexico. The dogs look as nervous as their tiny stature might make them feel. The remarkable point here is both breeds, as varied in size, look and behaviour as they could be, originated from a single ancestor, the wolf.

The largest ever genetic family tree of dogs and wolves was constituted by ecologists and evolutionary biologists from the University of California in Los Angeles (ucla) in usa, piquing the interest of scientists and dog-lovers alike. The study says dogs were born in West Asia—Israel, Saudi Arabia and Iran. This find, published in Nature on March 17, contradicts previous talk that gave the dogs an East Asian or Chinese origin. “Besides, there never was a hint in the archaeological record that dogs evolved there (East Asia),” said Robert Wayne, lead researcher.

There is no fixed date as to when dogs were domesticated; through the various studies and archaeological records the timeline was narrowed down between 15,000 to 40,000 years ago. Some 31,000-years-old dog remains have been found in Belgium and remains 12,000 years old were found in the West Asian region. To do away with the confusion here, the researchers studied both maternal and paternal heritage. Previous research usually examined mitochondrial dna inherited from the mother. Wayne’s team analyzed 48,000 dna markers scattered across genomes of 85 dog breeds as well as 200 grey wolves from 11 different populations around the world. dna in 80 per cent of the dogs matched that of wolf from West Asia and neither Belgium nor the Russian wolf, thus clearing doubts.

“This gives us the fine-scale resolution to analyze how these breeds are related to one another and to wolves,” said John Novembre, member of ucla’s Interdepartmental Program in Bioinformatics and part of the study.

That’s not a herder

The family tree puts the much-revered German Shepherd closer to the calm, “black mask” wearing mastiffs, the stocky boxers and other guarding dogs. But as the very name suggests, the Shepherd has been used to herd sheep. The fleet greyhound, Irish wolfhound and the lumbering Saint Bernard count herding dogs among their closest kin. The Pharaoh and Ibizan hound, often called the oldest of furless breeds, are recent constructions, actually.

Short-legged dogs like dachshunds and basset hounds have one unique gene—the mutant growth-factor gene. Similarly, there are unique genes for small size, different fur types and different coat patterns and colours. “It seems that in dogs, the different appearances add to just a handful of genes,” Wayne said. A small number of genes can thus be tweaked to create an amazing diversity of forms and sizes in dogs.

In a separate paper, Melissa Gray, doctorate in dog evolution from ucla, discovered the gene igf1 responsible for small size in dogs. She analyzed which wolf populations are closest evolutionarily to this gene. The findings, published in bmc Biology in February, show the gene arose in West Asian wolves, giving further support to the claim made by Wayne’s team. Reduction in body size is a common feature of domestication as seen in cattle, pigs and goats. “Small size could have been more desirable in more densely packed agricultural societies, in which dogs may have lived partly indoors or in confined outdoor spaces,” said Gray.

Breeders’ secrets

Eighty percent of dog breeds are products of controlled breeding practices largely developed in the Victorian era in the 19th century.

Ancient breeds such as the Afghan hound and the American eskimo—that appeared 500 years ago and are still kept as pets—have genetic signatures indicating interbreeding with wolves, but modern dogs only have dog genes in them. “The strict rules that have been in place since Victorian times to maintain breed purity must play a key role in making sure wolf dna does not make it into the domestic dog lineage,” said Beth Shapiro, evolutionary biologist at Pennsylvania State University in usa.

Wayne suggested the research could be used to create a genetic gold standard for any breed. Dipak Saha, dog breeder in Kolkata, said dog breeding is a high-profit business. “300-500 dogs worth one million rupees are sold in Kolkata every month.

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