An international team of genome laboratories from North America, Europe and Japan has created a unified gene map that establishes the location of more than 16,000 human genes. The map represents the first edition of the quintessential goal of the Human Genome Project--a catalog of all the genes that make up a human being--and provides the location of one in five of all human genes.
"This gene map and its future editions will provide geneticists the biological equivalent of a chemists' periodic table-a systematic and universal frame of reference that will speed the discovery of genes underlying inherited human diseases," said Dr. Eric Lander, a member of this consortium and director of the Whitehead/MIT Center for Genome Research. "With such a map, searching for a disease gene should no longer take years of painstaking effort. Instead, geneticists will be able to simply scan the human genome for an inventory of all the genes, or candidates, in a suspected region and identify the culprit."
Gene maps will also become essential for searching the genetic basis of complex diseases, such as diabetes and cancer, that are caused by the interaction of several genes and the environment. The new gene map is described in the October 25 issue of Science by more than 100 authors representing the international consortium. The National Library of Medicine has also released a new Web site that incorporates this information in a consumer-friendly format. The URL is .
"A map like this has tremendous value for identifying disease genes and provides extraordinary opportunities for a new era of medicine. Given this, and the wealth of information we have collected so far on the human genome, it seemed a shame to wait until the entire genome is sequenced to put together a gene map," said Dr. Thomas Hudson, senior author on the paper and head of the Whitehead mapping team. "It made more sense to construct a series of increasingly comprehensive gene maps that geneticists around the world can put to good use."
FULL MAP IN NINE YEARS
The Human Genome Project has established a goal of completing the gene map and sequencing the 3 billion DNA building blocks by 2005. The unified gene map, put together in the past 18 months, attains one-fifth of this goal and ensures that researchers will be able to achieve the goal comfortably.
A major contribution to this effort came from the Whitehead Institute. Last year, Whitehead and Genethon announced a comprehensive map of more than 15,000 landmarks called sequence tagged sites or STSs that span 95 percent of the human genome. The integrated map provided researchers the framework for the gene map. Of the 16,000 human genes mapped in this paper, more than 9,000 were mapped at Whitehead.
The work reported in this paper greatly increases the number of mapped human genes. At the end of 1994 there were a little more than 5,000 mapped human genes according to the Genome Data Base. The number of mapped genes has tripled in the last 22 months since this project started.
This first-edition map also reveals some interesting, albiet preliminary, details about the distribution of human genes among the 23 chromosomes. The researchers observed, for example, that chromosomes 1, 17 and 19 were gene-rich and that chromosomes 4, 13, 18, 21, and X were gene poor-a finding consistent with those in the earlier Whitehead map.
One of the foremost applications of the gene map will be in positional cloning-a method commonly used for searching disease genes. In this time-consuming method, researchers study a number of affected families to narrow the location of the disease gene to a specific region on a given chromosome. They then use the several pieces of overlapping DNA clones within the suspected region to identify genes contained in the region. These genes are then scrutinized for the presence of sequence mutations in affected individuals.
"By providing an inventory of all candidate genes within that region, gene maps will make positional cloning more efficient," said Dr. Lander. But the value of gene maps will extend beyond facilitating gene searches. They will shed light on genome organization, provide information about clustering of related genes, and tell us more about conservation of gene order among species.
Editor's note: See the next issue of Tech Talk for a preview of the "post-genome world" based on a Science policy article by Dr. Eric Lander.
A version of this article appeared in MIT Tech Talk on October 30, 1996.