It is the substance that determines our sex.
When defective, it binds parents and children with a legacy of shared suffering from genetic diseases like hemophilia or fragile X syndrome, a leading cause of mental retardation.
And yet, it's geography has been as mysterious to us as the hinterlands of Asia and Africa were to an earlier generation of explorers. Until now. In an article published Friday, researchers from Washington University School of Medicine announced they have achieved a genetic milestone - completion of the first high-resolution map of chromosome X. No other chromosome has been described with this degree of specificity, the researchers say. It is as if they have mapped a road from St. Louis to San Francisco, describing a landmark for every mile of the trip. With the map to guide them, other researchers should more quickly accomplish their goal of identifying disease genes, which along with other genes that control specific inherited traits are located along the chromosome. "I'm very excited about this. This is a big landmark," said Dr. William S. Sly, chairman of the Department of Biochemistry and Molecular Biology at St. Louis University Medical School, who reviewed a summary of the study. To the uninitiated, the chromosome map may seem like nothing more than a curiosity. But because the X chromosome is so closely identified with several important genetic diseases, Sly said its mapping would have a great impact on the lives of many people. "To people who have a child with a birth defect, for instance, its tremendously important for them trying to understand the prospects for that child and for their future children," Sly said. "When you see those people, suddenly this kind of genetic discovery becomes very important." A chromosome is a double strand of DNA that is in the nucleus of every cell. Humans have 23 pairs of chromosomes. Within them are encoded instructions for all our genetic traits - everything from our sex to our susceptibility to certain diseases. …