The final sequence of chromosome 6 has been analysed and announced. Weighing in at just over 166 million bases, it is the largest human chromosome to be analysed and published so far. Its genetic make-up is revealed in Nature (Vol. 425, No. 6960, 23 October 2003, pp. 805-811).
A. J. Mungall and colleagues unravelled the genetic giant, which forms a little less than 6% of the entire human genome. Of its 2,190 genes, 633 are inactive blasts from the past. The remaining 1,557 are thought to be functional. Of these, around half have not previously been described and their roles are unknown.
Chromosome 6 is most famed for the major histocompatibility complex (MHC), a previously sequenced region that is involved in the immune response. Other landmarks include the PARK2 gene, which is involved in a juvenile-onset form of Parkinson's disease, and the HFE gene. Mutations in the latter cause hereditary haemochromatosis, a condition affecting 1 in 400, which results in organ failure. The chromosome also contains the largest cluster of transfer RNA (tRNA) genes. tRNA helps to translate the DNA sequence into proteins.
This is the seventh human chromosome to be sequenced, joining the ranks of 20, 21, 22, 7, 14 and Y. "A finished chromosome 6 reveals an abundance of biological information previously buried within the draft of the human genome assembly," say Jane Grimwood and Jeremy Schmutz in an accompanying News and Views article.
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