Chromosome 6 unravelled 23/10/03. By the Wellcome Trust Sanger Institute The DNA sequence of chromosome 6, which constitutes about 6 per cent of the human genome, has been completed by researchers from the Wellcome Trust Sanger Institute.

The seventh of the 24 human chromosomes to be completed - joining chromosomes 7, 14, 20, 21, 22 and Y – chromosome 6 is the largest to be fully analysed to date.

Chromosome 6 was already known to include genes with implications for cancer, heart disease and mental health. The new analysis has more than doubled the number of genes accurately identified on the chromosome.

See chromosome 6 in the interactive chromosome browser [requires Flash]

Key features of chromosome 6

• The sequence is 166 880 988 base pairs - equivalent to about 50 bacterial genomes.
• The chromosome contains 1557 genes.
• Less than 50 per cent of genes on chromosome 6 were known before.
• The most variable human gene - HLA-B - is on chromosome 6. It is involved in immunity.
• More than 130 000 sequence variants (SNPs) were identified during the project. Some SNPs are important for disease and diagnosis.

The researchers have already identified 130 genes on chromosome 6 that cause, predispose or protect humans to certain diseases. For example, mutations in the HFE gene cause hereditary haemochromatosis, an iron overload disorder, while the PARK2 gene is associated with a juvenile-onset form of Parkinson's disease.

Background: Hereditary haemochromatosis

The most gene-rich and the most variable part of the genome is that of the major histocompatability complex (MHC). The MHC plays a crucial role in our immune system - our biological defence against microbes - as well as in transplant biology, determining our match against potential donors.

Stephan Beck, immunologist and Head of Human Sequencing at the Wellcome Trust Sanger Institute, said: "The MHC helps discriminate between our own cells and those of 'invaders', such as bacteria. If this delicate balance is disturbed it can result in autoimmune disease such as type 1 diabetes, rheumatoid arthritis and multiple sclerosis. Autoimmunity is complex and affects about 4 per cent of the population. The sequence of chromosome 6 will help to advance research into these human diseases."

Image credit: Wessex Regional Genetics Centre

Further reading

Mungall AJ, et al. The DNA sequence and analysis of human chromosome 6. Nature 2003, 425, 805 – 811. Abstract