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Last Updated: Thursday, 25 September 2003, 18:00 GMT 19:00 UK
'Walkies' through dog genome
By Jonathan Amos
BBC News Online science staff

Scientists have had a fast read through of the dog genome, the code that describes how man's best friend is put together.

Shadow, Tigr
Shadow is a nine-year-old standard poodle
It is not a complete guide to canine genetics - that will come later - but the study has thrown up some interesting facts that will prove useful pointers for researchers looking into human and animal disease.

One such nugget is the realisation that 75% of the genes we think are in humans also appear to be in dogs.

And perhaps not surprisingly there is also clear evidence substantial numbers of canine genes are employed by the olfactory system - the animal's sense of smell.

"We estimate the dog looks more like the mouse in terms of the number of its olfactory receptors but it also appears that the dog may also have unique subfamilies of these receptors," Dr Ewen Kirkness, one of the scientists involved in the study, told BBC News Online.

Personal poodle

The biological samples used for this research came from a poodle called Shadow.

The double-stranded DNA molecule is held together by chemical components called bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
Groupings of these letters form the "code of life"; there are estimated to be about 2.4 billion base pairs in the dog genome wound into 40 distinct bundles, or chromosomes
Written in the DNA are possibly 30,000 genes which dog cells use as templates to make proteins; these sophisticated molecules build and maintain the animal's body
It is one of three dogs belonging to Dr Craig Venter, the US researcher who led the private effort to sequence the human genome.

He funded his own Center for Advancement of Genomics and The Institute for Genomic Research (Tigr), both in Maryland, to work together on the project.

The centres looked at about 80% of the bases, or "letters", that make up the DNA found in dog cells.

The nature of their approach, however, meant the examination was very rough and the results are likely to contain many errors.

Certainly, the full Dog Genome Project, led by US National Human Genome Research Institute (NHGRI), is already on course to achieve far greater detail and accuracy.

Nevertheless, by using guiding information already available from the human and mouse genomes, the Maryland scientists say they were able to pull out useful data from the poodle effort.

Specific breeds

It can be shown, for example, that the dog lineage was the first to diverge from the common ancestor of men, mice and dogs - although the human and the dog are much more similar to each other at the genetic level than to the mouse.

"This is down to the differences in the mutation rates in the three species - the mouse's is much faster. So, in terms of time we are closer to the mouse; in terms of sequence we are closer to the dog," Tigr researcher Dr Kirkness said.

Bess dog, BBC
Labrador: The individual breeds are highly defined populations
The study also identified 974,400 of what are termed single nucleotide polymorphisms (SNPs) in the dog.

These are tiny genetic variations that are important in understanding the genes that contribute to diseases and traits among various breeds of dogs - and therein lies the driving force behind having a complete canine genome.

Dogs are known to suffer from about 400 inherited diseases, most of which have homologous conditions in humans, and some of which are not represented in the laboratory mouse.

Other species

What is more, pedigree dogs are highly defined. They are just like isolated human populations - a closed gene pool.

"This, together with the fact that almost any two dogs can be bred to give a fertile offspring, makes the animal a very powerful tool to study genes that are responsible for diseases and traits," said Dr Kirkness.

Throw in the high level of medical monitoring today's dogs enjoy and it is easy to see how probing the canine genome can have real spin-offs for the understanding of human health and behaviour.

"Dogs get narcolepsy, for example," said Professor James Scott of the Genome Institute in the UK. "We found the gene for human narcolepsy by looking at Dobermans.

"With Dobermans you can clap your hands and they will all fall asleep in a pile. It's rare but very curious and important for understanding sleep patterns."

More for the money

However, the real point of the Tigr/TCAG exercise was a proof of principle one, Dr Kirkness said.

By using a "rough sketch" approach, science could take a glimpse at the many mammalian genomes deemed interesting but which would never receive funding for a full-scale decoding effort, he added.

"Even for higher-level coverage, complete sequencing can now be done in a year," Dr Kirkness explained. "But for the level of coverage we report with the dog, you could envisage doing half a dozen mammalian genome sequences a year."

It is a point echoed by Dr Stephen O'Brien from the US National Cancer Institute: "NHGRI recently estimated that in the next four years, US sequencing centres alone could produce 460 billion bases - the equivalent of 192 dog-sized genomes at [just under the Tigr/TCAG] coverage."

Commenting on the latest work, Dr Matthew Binns, a UK dog geneticist, said: "This will be useful in studying common diseases such as cancers and heart disease. But it will be superseded in a few months' time when we're expecting the public Dog Genome Project to be completed."

Dr Ewen Kirkness, Tigr researcher
"Dogs suffer from many genetic disorders that resemble human conditions"

Professor James Scott of the Genome Institute
"We will have better treatments, better predictions and ultimately, better health"

Human genome finally complete
14 Apr 03 |  Science/Nature
Mouse clues to human genetics
04 Dec 02 |  Science/Nature
Origin of dogs traced
22 Nov 02 |  Science/Nature
Plans to decode dogs
27 Sep 02 |  Science/Nature

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