Scientists Near DNA Breakthrough
LONDON (AP) _ An international team of researchers says it is on the verge of unraveling for the first time the genetic pattern of a human chromosome _ a milestone toward what experts call one of the most important scientific accomplishments ever.
The team, involving British, U.S. and Japanese scientists, is part of a worldwide collaboration known as the Human Genome Project, which aims to reveal the structure of the estimated 100,000 genes in human DNA.
That will help scientists better understand what can go wrong in the body and how to fix it.
The group investigating chromosome 22 _ the second smallest of the 24 kinds of chromosomes that carry human DNA _ is putting the finishing touches on its work and plans to submit it for publication in the journal Nature later this year, team leader Ian Dunham said Thursday.
``We have it completed now to the point where there isn’t anything else we can do. We are now working on the analysis,″ said Dunham, senior research fellow of the Sanger Center in Cambridge, England, which is handling about a third of the entire genome project.
Genes are arranged in tightly coiled threads of DNA organized into pairs of chromosomes in every cell of the body.
Genes can promote or cause disease when they don’t work properly. Some of the illnesses linked to genes gone bad include cancer, arthritis, diabetes, high blood pressure, Alzheimer’s and multiple sclerosis.
Chromosome 22 contains genes involved in the immune response, schizophrenia, heart defects, mental retardation, leukemia and several other cancers, said Bruce Roe of the University of Oklahoma, part of the team examining it.
The team, which also involves Keio University in Japan, Washington University in St. Louis and scores of labs across the world, is revealing the sequence of the building blocks of DNA along the length of the chromosome.
Matt Ridley, head of the England-based International Center for Life and author of the recently published book ``Genome,″ described the imminent completion of the chromosome 22 sequence as a milestone on the way to decoding all the human DNA.
``The whole project, once it’s completed, will be one of the most significant scientific achievements of all time,″ he said. ``It’s the instruction manual for our species, the complete guide for how to build and run the human body.″
Scientists hope eventually to use the knowledge to help them find the causes, cures and prevention of the thousands of genetically influenced diseases afflicting mankind.
``The important thing about this chromosome is that although it is a small chromosome, it is probably one of the richest in genes and one of the most active in diseases,″ Roe said.
Roe said there now are nine small gaps in the sequence of the chromosome, because of difficulties maintaining the DNA in a stable enough state to analyze it in the laboratory.
``In two weeks’ time, we expect to get that down to six or seven (gaps),″ Roe said.
The scientists don’t know whether the gaps contain any important genes or just repetitions of what they already have found, but Dunham said the missing pieces are very small.
He said current technology would not allow the team to fill all the gaps and that the same problem likely will occur with the deciphering of other chromosomes.
Dr. Francis Collins, director of the U.S. National Human Genome Research Institute, said scientists in the field have agreed that a chromosome can be considered completely sequenced once every closable gap has been shut.
The sequencing project also omitted some regions on each end of the chromosome that contain long repeated DNA sequences. Bits of these regions were sequenced to confirm the presence of these repeats.
About 29 percent of the human genome _ all the DNA in our chromosomes _ has been sequenced so far by the international collaboration, experts say.
A first draft of the complete human genetic pattern, listing about 90 percent of the genes, is expected by next spring and a final map filling in the gaps is scheduled for completion by 2003 or sooner.
Collins predicted that once the chromosome 22′s strategy is published, the teams working on other chromosomes will adopt it, which will speed the entire project to the finish line earlier than expected.
Besides the international effort, the Rockville, Md.-based Celera Genomics also is sequencing human DNA and predicts it will finish in 2001.