Four years after publishing a draft of the human genetic sequence, researchers have hit the halfway mark in producing the "gold standard" version.
They have just published a detailed run-down of the 12th chromosome - known as chromosome five - which means there are just 12 left to complete. Chromosome five is the largest so far, with 923 recorded genes, of which 66 are involved in human disease.
The chromosome, which was sequenced by US scientists, is detailed in Nature. It is the second of three chromosomes that the Department of Energy Joint Genome Institute (JGI) has finalised in collaboration with colleagues at the Stanford Human Genome Center (SHGC).
Code breakers
Cracking the human code has been a bit like painting a picture. First comes a rough sketch followed by a slightly fuller version before, finally, the minute detail is added.
When the draft version of the human genome was unveiled in June 2000, 97% of the "book of life" had been read. Then, last year, scientists announced the decoding was almost 100% complete. Now, several institutions around the world have divided up the 24 human chromosomes - the cellular structures into which DNA is wound - and are going through them with a fine-tooth comb for a final time, to fill gaps and correct errors.They are, as it were, dotting the i's and crossing the t's and giving the whole sequence a thorough spell-check.
"It is about getting everything in the right order," commented Dr Tim Hubbard, of the Human Genetics group at the Sanger Institute in Cambridge, UK. "In the draft version there were 100,000 gaps in the whole genome. It was a small percentage of the sequence, but it meant you were uncertain about the order of the pieces. "It is important for doing experiments to have the complete sequence - to have no gaps at all."
Giant chromosome
According to researchers at the JGI and SHGC, the landmark chromosome five is a genetic behemoth, containing key disease genes and a wealth of information about how humans evolved.
"This extremely accurate sequence will be a powerful tool for scientists trying to understand human disease," said US Secretary of Energy, Spencer Abraham. The giant chromosome is made up of 180.9 million letters - the A's, T's, G's and C's that make up the genetic code.
Of the 923 genes that sit on chromosome five, 66 are known to be linked to disease when they go wrong. Another 14 diseases seem to be connected to chromosome five genes, but they have not been linked to specific genes yet. Having a detailed picture of chromosome five will be an immense help to researchers investigating these illnesses.
"It is very useful to have a base sequence which you can then compare individuals to," Dr Hubbard told BBC News Online. "Then you can look for key differences between people that do have the disease and people that don't have the disease." Another feature of chromosome five will peak the interest of scientists studying the difference between humans and chimpanzees.
Despite great similarities between the genomes of the two species, there are some key structural variations. In particular, one large section of chromosome five is flipped backwards in humans compared with chimps. Such an inversion makes it impossible for the two chromosomes to pair up during reproduction, which could have driven a wedge between the evolving ancestral populations.
"Junk" DNA
It is not just the genes in chromosome five that the scientists are interested in. Volumes of genetic material lie in between the genes, which for a long time were dismissed as "junk" by researchers. But on closer inspection, it seems this judgement was premature. The fact that sequences of junk were conserved for hundreds of generations, suggests they have a function worth holding on to.
"Important genetic motifs gleaned from vast stretches of non-coding sequence have been found on chromosome five," said Eddy Rubin, JGI's director. "Comparative studies conducted by our scientists of the vast gene desert... have shown these regions, conserved across many mammals, actually have a powerful regulatory influence."
Over the next few months, the remaining 12 human chromosomes should be completed to a final gold standard of accuracy. Dr Hubbard concluded: "Several groups are working on the remaining chromosomes - tidying them up - and they should all be complete by the end of the year."
Archived topic from Anythingforums, old topic ID:1007, old post ID:11975
Human genome hits halfway mark
Human genome hits halfway mark
im curious as to what all the 'junk' really says.
Archived topic from Anythingforums, old topic ID:1007, old post ID:14597
Archived topic from Anythingforums, old topic ID:1007, old post ID:14597