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Genetic milestone

4 December 1999

One down, 23 to go. Chromosome 22 has become the first human chromosome whose
DNA sequence is known in full, except for a few minor gaps. Ian Dunham,
coordinator of the international sequencing project at the Sanger Centre in
Cambridge, estimates that the chromosome contains 800 or so genes. The
33.5-million-base sequence includes a continuous strand of 23 million bases, the
largest single chunk of DNA ever logged (Nature, vol 402, p 489). The
sequence includes gaps where it was impossible to clone the DNA using
bacteria.