In December 1999, the HGP completed the first finished, full-length sequence of a human chromosome - chromosome 22. This accomplishment demonstrated the power of the HGP method of clone-by-clone sequencing to obtain large amounts of highly accurate sequence. In the clone-by-clone approach, clones of human DNA, such as bacterial artificial chromosomes (BACs), that have a precisely known location on a physical map are the starting points for DNA sequencing reactions. Researchers chose to finish chromosome 22 first because it is relatively small and because highly detailed maps of 22 had already been constructed.
The sequence of chromosome 22 gave scientists their first ever view of the organization of an entire chromosome. The sequencing effort concentrated on the long arm of the chromosome. Each chromosome consists of two "arms", a short arm (called "p" for "petite") and a long arm (called "q"). In the case of chromosome 22, the q arm happens to be very rich in genes. The sequence from the long arm is 33,400,000 base pairs in length, and contains at least 545 genes.
Dunham, I., Shimizu, N., Roe, B.A., Chissoe, S., Hunt, A.R., Collins, J.E., Bruskiewich, R., et al. The DNA sequence of human chromosome 22. Nature, 402: 489-95. 1999. [Full Text]
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Last Reviewed: May 28, 2013