It is a fact that 75% of our genetic make-up is the same as a pumpkin.

Although we like to think we are special, our genes bring us down to Earth. DNA is what ties the entire living world together. It may well account for the extraordinary diversity among organisms but it also serves to underline their common origins - we all evolved from the same soup of chemicals.

So while a complete map of the human genome - our particular collection of genes - will be extremely useful when it is finished in the next few years, that will not be the end of the story.

Once we have the map, we will need something to compare it with. And that is the goal of an emerging field of research called comparative genomics. By studying non-human genomes, we gain insight into our own.

Dogs in the mirror

Elaine Ostrander is analysing the dog genome to help identify genes for disease in humans.

The Sanger Centre is helping to map the human genome

"Dogs really mirror humans in many many ways," says the geneticist who works at the Fred Hutchinson Cancer Research Center in the USA.

"Dogs get the same diseases we do, they live in the same environment we do, they're exposed to the same potential carcinogens - cancer causing chemicals - they often eat the same food that we do.

"And they manifest diseases in a similar way to humans. So we know when we're studying dog diseases, that we're often studying really good models for particular human diseases."

Insight into breast cancer

Dogs and humans share genes for a number of illnesses: blindness, epilepsy, and some cancers. Dr Ostrander's work has already provided an insight into one form of breast cancer.

Gene machine: Sequencing equipment is getting faster

"A couple of years ago, my lab cloned and sequenced the canine BRCA1 gene. And you may recall that the BRCA1 gene is the gene that was identified in humans that, when mutated, causes very strong susceptibility to breast cancer.

"And we were interested in seeing if dogs had that gene, and if so, how similar was it to the human gene. And in fact, when we cloned it and sequenced it, it was extraordinarily similar - something like 85% identical."

So the sequence in dogs may well reveal how the disease takes hold in humans.

Worm leads the way

Other scientists are in the process of sequencing the genomes of rats, cats, mice and pigs. Several simple organisms such as viruses and bacteria have already had their entire genetic blueprints sequenced.

C elegans: A scientific first

In animal terms, the big breakthrough last year with the completion of the genome of worm Caenorthabditis elegans, the tiny worm that lives in soil.

"C Elegans was the first multi-cellular animal to be sequenced," says Dr Patricia Kuwabara of the UK's Sanger Centre. "In part, it's because it had a small genome.

"There were also very good researchers who had the vision to see that sequencing an entire organism would lead to a lot of discoveries about basic biology, and may also provide insights into how genes are regulated in vertebrates such as ourselves."

Apes and humans

The worm's genetic blueprint has already proved useful in the study of the human brain condition Alzheimers disease.

But there is more to comparative gemonics than just provding clues to genetic influences on diseases. It also lets us ask fundamental questions about human and animal minds. Dr Walter Messier, from the American genetics company Genoplex, is looking for the differences between the human and chimpanzee genome.

"We have unique cognitive abilities that don't show in the great apes, our close relative," he says. "So by looking at the specific genes and proteins that they code for, the goal is to determine how those proteins have changed in humans, and there by get some idea of our cognitive abilities."

The human and chimpanzee genomes are almost identical, with a mere 1.5% difference between the genetic codes. What makes humans human and chimps chimps can be put down to relatively few genes. These are what Walter Messier calls the critical genes and it would be a huge advance to identify them.