UK scientists have finished an in-depth study of chromosome six, the seventh human chromosome to be analysed in detail. The team, from the Wellcome Trust Sanger Institute in Cambridge, say the chromosome is made up of nearly 167 million base-pairs - chemical 'letters' of DNA - which means that it accounts for nearly six per cent of the entire human genome. They found 1557 working genes along its length, only 772 of which had been identified previously. They include genes involved in haemachromatosis, an iron overload disorder, and a type of Parkinson's disease that affects children.
An international consortium unveiled the final version of the entire human genome on 14 April 2003. Researchers have since been looking at each of its 24 different chromosomes in detail, to identify the 'coding' stretches of DNA that make up genes. As well as chromosome six, scientists have also published complete, fully-analysed sequences for chromosomes 22, 21, 20, 14, 7 and the Y chromosome. Chromosome six is best known for being home to a large cluster of genes that play a vital role in the body's immune system. The sequence of this important region, called the major histocompatibility complex (MHC), had already been published in 1999. But the authors of the new study, published in Nature last week, say the chromosome also contains genes 'directly implicated in cancer, schizophrenia and autoimmune diseases'.
An article accompanying the paper said: 'The finished sequence of human chromosome six reveals an abundance of biological information previously buried within the draft of the human genome'. It also pointed out that the increasing availability of genome sequences from other species is making it easier for researchers to pick out the important 'coding' DNA sequences that make up genes. Using computer programs, the chromosome six team compared human DNA with that of the mouse, rat, pufferfish and zebrafish, to pick out stretches of sequence that have been preserved intact throughout evolution. Such 'conserved sequences' are likely to be part of genes, rather than the large tracts of 'non-coding' DNA found in between genes. The power of this approach, called comparative genomics, will grow as more animal genomes are decoded, say authors Jane Grimwood and Jeremy Schmutz, of the Stanford Human Genome Center in the US.