Gene mappers have announced that they have nearly finished decoding the genetic blueprint of the fruit fly. It is an important step that will also help scientists understand human genes.

Fruit flies or Drosophila are used extensively in biology. Thousands of scientists around the world use them to study genetics and developmental biology.

They are ideal organisms. They are easy to grow, not too small and live only two weeks. They are considered so important that the scientists who established their significance won a Nobel prize in 1995. Importantly, they share most of their genes with humans.

United States company Celera Genomics has announced that it has determined the genetic code of the fruit fly but still has to assemble the genes into the correct order.

'Shotgun' method

"Over 1.8 billion base pairs, letters of genetic code, were sequenced," the company said.

Remarkably the company said it only started the work on the tiny fly, known to scientists as Drosophila melanogaster, in May.

Drosophila chromosomes

To get the blueprint, Celera scientists have used a controversial "shotgun" method to map genes. Rival scientists say that technique can miss important bits of the sequence. But Celera says the method catches everything that matters.

"The completion of Drosophila will validate the effectiveness of Celera's whole genome shotgun approach in deciphering complex genomes," J. Craig Venter, president of the company, said.

"By comparison, the first genome of a free-living organism, the bacterium Haemophilus influenzae, consisting of two million letters of genetic code, took one year to complete, and other early genomes not using Celera's whole genome shotgun strategy took over a decade to complete," a statement from the company said.

There is still work to be done on the fruit fly, Venter points out, "What's done is the sequencing phase, akin to gathering all the pieces of a jigsaw puzzle. Now they have to put them together. We have to close the gaps."

More complex

It is estimated that the fruit fly will have anywhere between 12,000 and 20,000 genes - humans have between 80,000 and 100,000 genes. Until now, the most complex organism that has been sequenced is the flatworm, C. Elegans. Drosophila is a much more complex animal, having a central nervous system.

Although insects are clearly very different from humans, on a genetic level we have a great many things in common.

After sequencing Drosophila, Celera has said it will now turn its full attention to the human genome.

"On the Tuesday after Labour Day, we switched everything 100 percent to sequencing the human genome," said Venter.

"Between now and the end of the year we will have covered at least 70 percent of the human genome and by early spring, by February or March, we should have 90 percent of it covered."