US researchers have unveiled a complete 'gold-standard' version of the DNA sequence of human chromosome five. Consisting of 181 million base-pairs (chemical 'letters') of DNA, chromosome five is the largest human chromosome analysed in detail to date. However, despite its size it contains relatively few genes - just 923 - compared to the 1461 found on chromosome 19, which is less than a third of the size. The scientists, based at the Department of Energy Joint Genome Institute (JGI) and Stanford Human Genome Center, think that some of the 'spare' chromosome five DNA plays a crucial role in controlling the activity of other genes.
An international consortium unveiled the final version of the entire human genome on 14 April 2003. They found that it is made up of 2.9 billion base-pairs of DNA, and contains an estimated 25-30,000 different genes. Researchers have since been looking at each of its 24 different chromosomes in detail (numbers 1-22 plus the X and Y sex chromosomes), to identify the 'coding' stretches of DNA that make up these genes. They have also been filling gaps - stretches of DNA sequence that could not easily be determined - and double-checking for any errors. Chromosome five is the twelfth chromosome to be analysed in detail, with the remaining twelve due to be completed by several different groups by the end of the year.
Of the 923 genes identified along the length of chromosome five, 66 are already known to be involved in human disease. Having the full chromosome five sequence should speed up the search for at least another 14 genes involved in inherited disorders. But it seems that the DNA in between the genes - previously dismissed by some researchers as 'junk DNA' - will also yield important information. 'Comparative studies conducted by our scientists of the vast gene desert where it was thought there was little of value have shown that these regions, conserved across many mammals, actually have powerful regulatory influence', said JGI director Eddy Rubin.
Sources and References
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Disease Genes, Important Regulatory Elements Populate Vast Terrain On Human Chromosome 5
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Human genome hits halfway mark
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Scientists map Chromosome 5
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The DNA sequence and comparative analysis of human chromosome 5
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