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DURHAM, N.C. -- A team of British and American scientists has completed the detailed genetic mapping of human chromosome 1, the largest single unit of genetic material in the human genome and the final chromosome to be completely sequenced.

Researchers at the Wellcome Trust Sanger Institute and Duke University Medical Center led the effort, which involved more than 150 scientists and took about 10 years to complete.

"This achievement effectively closes the book on an important volume of the Human Genome Project, which was started in 1990 to identify the genes and DNA sequences that provide a 'blueprint' for human beings," said Simon G. Gregory, Ph.D., assistant professor at the Duke Center for Human Genetics and lead investigator on the study.

"Armed with this new information, researchers now have new tools for probing fundamental biological questions and examining the genetic factors involved in a range of diseases and medical conditions, including Alzheimer's disease, Parkinson's disease, cancer, autism and mental retardation," Gregory said.

The researchers will publish their findings in the May 18 issue of Nature. The study was funded by the Wellcome Trust and the Medical Research Council in the United Kingdom, and the National Institutes of Health in the United States.

The 23 human chromosomes -- the stringlike cellular structures that contain genes and other DNA sequences -- are made up of millions of chemical subunits called bases. The chromosomes are numbered from largest to smallest. Chromosome 1 makes up about 8 percent of the overall human genome, and it contains about twice as many genes as an average-sized chromosome.

In their study, the researchers determined that chromosome 1 contains 3,141 genes, roughly a thousand of which had never before been identified, Gregory said. Prior to joining the Duke Center for Human Genetics in 2003, Gregory led the chromosome 1 project at the Wellcome Trust Sanger Institute, which has sequenced more of the human genome than any other institution.

Chromosome 1 plays a critical role in human health and well-being, he said. Scientists have linked genetic mutations of the chromosome to more than 350 human diseases, and structural alterations of the chromosome are believed to contribute to a variety of mental retardation syndromes.

"Given the key roles of chromosome 1, the completion of this project has many exciting implications for the scientific and medical communities," Gregory said. "We are eager to apply this new wealth of genetic information about the composition and structure of the chromosome to important matters of health and disease."

Gregory's colleagues at Duke already have used information from the chromosome 1 sequence to identify genes associated with certain forms of Charcot-Marie-Tooth disease, a neurological disorder that causes loss of sensation to parts of the body.

In addition to mapping the chromosome's genes, the U.S.-U.K. team also identified almost 4,500 new single nucleotide polymorphisms (SNPs), or sections of DNA that vary slightly from the standard sequence. In previous work, scientists have identified 15 SNPs that influence the risk of developing diseases, including malaria, Gregory said. However, the functions of the newly identified SNPs have yet to be determined.

In another application, the new genetic map of chromosome 1 will help scientists to better understand the processes that contribute to genetic diversity among human populations, Gregory said.

The researchers found that the regions of the chromosome with the highest concentrations of genes also have higher rates of recombination -- "shuffling" of genetic material during reproduction -- than other areas. By examining such shuffling, scientists are able to gain a deeper understanding of the mechanisms that make us genetically different from our parents, and from one another, Gregory said. Loss or gain of certain regions of chromosome 1 during reproduction and cell division also are factors in the development of diseases and congenital conditions, and enhanced insight into these processes may ultimately lead to better screening and treatment options, he said.

Researchers already have used information from the HapMap Project, a large international effort focused on investigating patterns in human genetic variation, to look at variations in chromosome 1 among population groups from Europe, West Africa and East Asia. The researchers compared the prevalence of 68 SNPs in each of the groups and noted differences among the populations, Gregory said. These variations may provide clues to genetic distinctions among the population groups and to the selection pressures each group has faced through the centuries.

Researchers from the University of Washington-Seattle; the University of Oxford; King's College London; University College London; and Solexa Ltd. also participated in the chromosome sequencing project.