Chromosome 7 is the largest human chromosome to be sequenced so far. The analysis revealed that the chromosome has about 1,150 genes and 940 so-called 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.
"This work completes another volume in the genome encyclopedia at a high standard of quality and a high degree of continuity," says principal investigator Richard K. Wilson, Ph.D., director of Washington University's Genome Sequencing Center and professor of genetics and of molecular microbiology. "The sequence for chromosome 7 will be very useful for follow-up studies that have a medical application."
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.