Why dogs come in many forms
Steve Connor

The incredible diversity of dogs is encoded in their genomes

A poodle called Shadow and a boxer named Tasha have opened the door to understanding the fundamental nature of canine biology. Man’s best friend comes in so many shapes, sizes, colours and temperaments.

Scientists believe that the publication of the dog genome in the journal Nature will help to shed light on human as well as canine diseases as well as providing the definitive pedigree book for dog lovers.

Dogs were originally domesticated from the grey wolf in prehistoric times and selective breeding over many thousands of years has produced the most diverse range of individuals for any species of mammal.

Scientists believe that comparing the genomes of the 400 different breeds of dog will explain why some are aggressive guard dogs, some are good with children while others are just bred for their looks.

More importantly, comparing the dog and humans genomes could help scientists to understand the many diseases involving defective genes that affect both species.

"Of the more than 5,500 mammals living today, dogs are arguably the most remarkable," said Eric Lander, Professor of biology at the Massachusetts Institute of Technology and one of the leaders of the study.

"The incredible physical and behavioural diversity of dogs, from Chihuahuas to great danes, is encoded in their genomes. It can uniquely help us to understand embryonic development, neurobiology, human disease and the basis of evolution," Professor Lander said.

Two complete dog genomes — a standard poodle called Shadow and a boxer called Tasha — have now been deciphered. Scientists used this information as a genetic "compass" to search the genomes of nine additional breeds, including beagles, labradors, greyhounds and rottweilers, as well as wild canines such as the wolf and coyote.

"This work demonstrates a significant amount of variation that you can see between individual dogs at the genomic level," said Ewen Kirkness of The Institute for Genomic Research in Rockville, Maryland. "That variation can now be exploited to study the differences between dogs, their diseases, development and behaviours," Dr Kirkness said.

Selective breeding of dogs over the generations has had the unintended consequence of predisposing many breeds to genetic ailments, such heart disease, cancer, blindness, cataracts, epilepsy and deafness.

Using the dog genome, scientists hope to identify the genetic traits that lead to such predispositions, which should also help medical researchers investigating similar illnesses in humans, said Kerstin Lindblad-Toh of the Broad Institute of Harvard University and lead author of the study.

"The genetic contributions to many common diseases appear to be easier to uncover in dogs. If so, it is a significant step forward in understanding the roots of genetic disease in both dogs and humans," Dr Lindblad-Toh said.

Comparing different genomes has already revealed that humans share more of their genes with dogs than with mice, the standard laboratory species used in medical research.

The comparison has also enabled scientists to identify highly "conserved" regions of human DNA that appear not to have changed much during the long course of mammalian evolution — indicating that they serve a critical function in human development.

— By arrangement with The Independent

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