Gene map milestone as chromosome is decoded

Scientists have reached a milestone in their efforts to map the entire human genetic blueprint with the publication of the code for an entire chromosome. While this is but one of the 46 chromosomes needed to produce a human, it represents a mountain of information, containing more than 33 million individual pieces.

Details of the sequence of chromosome 22 were announced yesterday at press conferences in Washington, London and Tokyo organised by the science journal, Nature, and the US National Human Genome Research Institute. Nature publishes details of the sequence and how it was catalogued today.

The DNA "map" of chromosome 22 is part of an ongoing world scientific effort to catalogue the entire human DNA sequence or "genome".

While many smaller parts of the genome have been sequenced this is the first time that the sequence for an entire chromosome has been assembled. DNA is a marvel of compactness and every cell contains a complete copy of the human genetic blueprint, information which the cell uses to carry out its functions.

The DNA is neatly packaged into 46 chromosomes which are assembled in pairs. The chromosomes are, in turn, subdivided into a series of genes, the working parts of the DNA which produce all of the substances which keep us alive. We have about 100,000 genes which are shared out amongst the 46 chromosomes. Chromosome 22 is the second-smallest of the 46 and holds at least 545 genes and possibly as many as 1,000.

All of this is just numbers and unusable data unless researchers can find out what the genes do. Knowing the gene's sequence helps, however, to lead to an understanding of what it produces and how the chemical it makes contributes to life.

Natural variations in the DNA sequence of genes dictate variations in human appearance, skin and hair colour, weight and size. Some variations, however, have malign consequences, leading to illnesses such as cancer, Alzheimer's and schizophrenia.

Knowing the DNA sequence could help towards understanding many diseases. For example, there are at least 27 human disorders associated with changes to genes on chromosome 22.

The researchers also pointed out in their Nature report that of the genes sequenced on chromosome 22, at least 113 are also found in the mouse genome, compelling proof of nature's tendency to conserve useful parts of the DNA blueprint across different species.

The research teams who led the study also highlighted the World Genome Project policy of immediate release of newly detailed genetic sequences. A private sector group is also attempting to map the human genome but is not releasing all of the detail.