A primary goal of the Human Genome Project is to make a series of descriptive dia-grams—maps—of each human chromosome at  increasingly finer resolutions. Mapping involves (1) dividing the chromosomes into smaller fragments that can be propagated and char-acterized and (2) ordering (mapping) them to correspond to their respective locations on the chromosomes. After mapping is completed, the next step is to determine the base sequence of each of the ordered DNA fragments. The ultimate goal of genome  research is to find all the genes in the DNA sequence and to develop tools for using this information in the study of human biology and medicine. Improving the instrumentation and techniques required for mapping and sequencing—a major focus of the genome project—will in-crease efficiency and cost-effectiveness. Goals include automating methods and optimiz-ing techniques to extract the maximum useful information from maps and sequences.

A genome map describes the order of genes or other markers and the spacing between them on each chromosome. Human genome maps are constructed on several different scales or levels of resolution. At the coarsest resolution are genetic linkage maps, which depict the relative chromosomal locations of DNA markers (genes and other identifiable DNA sequences) by their patterns of inheritance. Physical maps describe the chemical characteristics of the DNA molecule itself.

Geneticists have already charted the approximate positions of over 2300 genes, and a start has been made in establishing high-resolution maps of the genome (Fig. 7). More-precise maps are needed to organize systematic sequencing efforts and plan new research directions.

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