The Human Genome Project: from mapping to sequencing

Until recently, the "human genome" programs were mainly directed towards the development of maps to identify disease genes. The genetic map comprises about 8000 highly informative second generation markers of the microsatellite type. The density of markers is now sufficient to localize a gene for a monogenic disease with a precision of 1 to 2 million base pairs easily, and to define intervals which contain susceptibility genes for multifactorial disorders. A third generation map based on single nucleotide polymorphisms that can be genotyped using DNA chip technology is in progress. The physical map, based on sets of overlapping yeast artificial chromosomes ordered using sequence-tagged sites, covers over 90% of the genome. However, this physical map cannot serve as a support for sequencing because of the numerous rearrangements that occur in yeast artificial chromosomes. An international network of laboratories has mapped a set of more than 30,000 expressed sequences from cDNAs using whole genome radiation hybrids that enable integration of genes within existing maps. The human genome program is now progressively shifting to massive sequencing, although sequence ready maps are not available for the major part of the human genome. Similarly, our capacity to interpret the available genomic sequence remains limited.