Mapping the Human Genome: Retrospective, Perspective and Prospective

The Human Genome Project (HGP) is a multinational effort to identify all the genes on the human chromosomes and to determine the sequence of the four kinds of nucleotide bases, abbreviated A, T, C, and G, in the DNA of both the coding and the noncoding parts of all the chromosomes. It is fundamentally a cartographic project: it aims not only to map all the genes on the chromosomes, but also to determine the ultimate map, the nucleotide sequence of the DNA. Hence, the HGP is an enterprise for complete mapping of the human genome. Genome is a hybrid word created by elision from genes and chromosomes, and that is what the word means. Human genome denotes the complete complement of genes and chromosomes in the nucleus of each human cell. The karyotype is a low-resolution optical microscope view of the human genome. The dimensions of the human genome are: (1) 24 types of chromosomes (the 22 autosomes and the X and Y chromosomes); (2) an estimated 70,000 genes (range of estimates, 50,000100,000) carried by those chromosomes; and (3) an estimated 3 billion nucleotides. (A small twenty-fifth chromosome is located in the mitochondria in the cytoplasm. It has already been sequenced completely with mapping of its genes and identification of disorders due to mutations in those genes.) The HGP was first formally proposed in 1985. It was debated, discussed, and planned during a five-year gestational period. In the United States, the project was initiated on 1 October 1990 and was predicted to take fifteen years for completion. On this schedule, the last gene and the last nucleotide should be identified by midnight on 30 September 2005. Today, six and a half years down the road, the project is said by Francis Collins, director of the HGP in the National Institutes of Health,