Sequence of human chromosome 7 finalised 10/7/03. By Washington University in St Louis School of Medicine The final, high-accuracy sequence of human chromosome 7 has been completed - joining the sequences of chromosomes 14, 20, 21, 22 and Y.

The findings are published in the 10 July 2003 issue of the journal Nature.

Chromosome 7 is the largest human chromosome to be sequenced so far. The analysis revealed that the chromosome has about 1150 genes and 940 'pseudogenes', stretches of DNA that closely resemble genes but contain some genetic change that prevents them from functioning like a gene. The biological significance of pseudogenes is unknown.

The work may benefit research in cystic fibrosis, deafness, B-cell lymphoma and other cancers, genes for which are found on chromosome 7. Also found there is the gene for P-glycoprotein, a protein that enables cancer cells to resist anticancer drugs. Other important genes found on chromosome 7 include those that help control cell division and cell death, genes for taste and smell receptors and those involved in immune responses.

Chromosome 7 also has a relatively centrally located centromere, a small region found on all chromosomes that is important during cell division. Centromeres on other chromosomes sequenced so far are located near the tip of the chromosome, like a knob. The centromere on chromosome 7 divides the chromosome into a short arm and a long arm, both of which carry many genes. Sequencing proceeded from each end toward the centromere.

The centromere itself contains many short repetitive DNA sequences and few, if any, genes.

The most challenging region of the chromosome to sequence was that containing genes for Williams-Beuren syndrome (WBS), a rare genetic disorder characterized by mild mental retardation, unusual facial appearance and a narrowing of the aorta, the major artery leaving the heart. The WBS region was difficult to decipher because it contains large segments DNA with many duplicated genes, and the number of duplicated genes differs among individuals. Children with WBS are missing long stretches of these duplicated genes.

"It seems that multiple copies of these genes are necessary for normal development, and if any are lost, developmental abnormalities occur," says Richard Wilson, Director of Washington University's Genome Sequencing Center. "People who study this disease may find the chromosome 7 sequence data very helpful."

Adapted from a news release by Washington University in St Louis School of Medicine .

Image credit: Wessex Regional Genetics Centre

Further reading

Hillier L W, Fulton R S, Fulton L A, et al. The DNA sequence of human chromosome 7. Nature, 10 July 2003. Abstract