Human Genome Project

Research scheme to map the complete nucleotide (see nucleic acid) sequence of human DNA. It was begun in 1990 and a working draft of the genome (a mapping of 97% of the genome, sequencing of 85%, and completion of 24% of the human genome) was achieved in 2000, with the results being published in February 2001. The publicly-funded Human Genome Organization (HUGO) coordinated the US$300 million project (the largest research project ever undertaken in the life sciences), which took place in over 20 centres around the world. In a competing effort, sequencing was also carried out commercially by US biotechnology company Celera Genomics, using the method of shotgun sequencing (breaking up the DNA into many small fragments, ordering the sequences of these fragments and then reassembling them). The completed detailed mapping of the genome was released on 14 April 2003. Since then, complete sequences of individual human chromosomes have been completed and published one by one.

In October 2004, researchers estimated that the human genome only contains between 20,000 and 25,000 different genes – far fewer than expected – and one gene may contain more than 2 million nucleotides. The knowledge gained from mapping all these genes is expected to help prevent or treat many crippling and lethal diseases, but there are potential ethical problems associated with knowledge of an individual's genetic make-up, and fears that it could lead to genetic discrimination.

Sequencing Each strand of DNA carries a sequence of chemical building blocks, the nucleotides. The different combinations of nucleotides code for the production of different proteins in the cell, and thus determine the structure of the body and its individual variations. To establish the nucleotide sequence, DNA strands are broken into fragments, which are duplicated (by being introduced into cells of yeast or the bacterium Escherichia coli) and distributed to the research centres.

Genes account for only a small amount of the DNA sequence. Over 90% of DNA appears not to have any function, although it is perfectly replicated each time the cell divides, and handed on to the next generation. Many higher organisms have large amounts of redundant DNA and it may be that this is an advantage, in that a pool of DNA is available to form new genes if one is lost by mutation.

Whose genome? The genome sequenced is not that of any one person. The HGP collected blood and sperm samples from a large number of donors and then processed the DNA of a small number (10–20) of these, ensuring that neither their scientists nor the donors would know whose DNA was finally used. As all humans share the same basic set of genes, the information gained will be applicable to everyone.

Further research in the ‘postgenomic’ era has been focussed on the medical relevance of the small genetic differences between individuals, such as single nucleotide polymorphisms, or SNPs. Valuable insights into human genetic diversity can also be derived from the comparison of our genome sequence with that of our closest relative, the chimpanzee, which was published in 2005.