The dog has been figured out

That closeness is reflected in the numerous diseases shared by dogs and humans, including cancer, heart disease, blindness, epilepsy and diabetes. Of the 10 most common diseases in dogs, eight are important to humans. The mapping offers the possibility that idiosyncratic dog breeds—specifically bred for behavioral traits such as obedience, viciousness and docility—may help illuminate the elusive genetic instructions that account for the variability of human personalities.

Tasha, a stout female with a brown-and-white coat and drooping jowls, was selected from a group of 120 dogs screened by the National Human Genome Research Institute in Bethesda, Maryland, US. The pure-bred boxer was chosen because her genes showed the least amount of variation among the candidates. Only female dogs were considered because they have two X chromosomes, which researchers wanted to map in detail. Scientists refused to say much about Tasha, the pet of an unidentified family. Her stoic photo, however, hangs prominently at the Broad Institute in Cambridge, Massachussetts, where the sequencing work was completed.

The researchers reported that the complete genome consists of 2.5 billion chemical letters—commonly known by the letters A, T, C and G—compared to about 3 billion for humans. In scouring Tasha’s genome and comparing it to genetic data from 10 other breeds, they catalogued more than 2.5 million specific differences that occur among dogs. Among mammals, dogs are a unique genetic specimen because of the intensive selective breeding that began only a few hundred years ago and created today’s roughly 400 breeds.

Their genetic architecture has made dogs particularly valuable for research. Scientists look for aberrant genes by comparing the DNA of subjects possessing or lacking a particular trait. When genes are contained in bigger haplotypes, they are easier to find. The researchers found haplotypes in dogs are 50 times bigger than those in humans, making it more efficient to hunt for disease-causing genes. Once a gene is identified in dogs, ‘‘it just takes a second’’ to find the equivalent gene in humans, Wayne said.

Dogs have already proved useful as proxies for humans in medical research. The gene that causes the sleeping disorder narcolepsy was first identified in Doberman pinschers and Labrador retrievers, and genetic defects associated with epilepsy came to light by studying pointers who suffered from the disease.