Human beings are very close to each other, sharing about 99.9 percent of their genome. Genes make up less than 5 percent of the human genome. Most of the DNA lies between the genes like a vast desert between strip malls. It's called junk DNA because nobody knows why it's there or what it's doing. Genes tell cells what proteins to produce, and proteins are the basis of all biological processes.
Several techniques exist to locate genes on a chromosome to create a physical map.
The technique has helped researchers find mutations that cause hereditary diseases, such as the gene for Huntington's disease . Dr. Nancy Wexler, Higgins Professor of Neuropsychology at Columbia, won the prestigious Albert Lasker Award for that discovery, made with colleagues at other institutions. Huntington's disease, a fatal neurologic disorder, is genetically determined. If a child inherits the gene for Huntington's disease, he or she will get the disease sooner or later. There are about 5,000 diseases with such straightforward genetic causes, but most are rare.