Each normal human sperm cell spells out sexual destiny by carrying either an X or a Y chromosome. But when these cells contain an extra sex chromosome or any other chromosome, called an autosome, the sperm's progeny can suffer myriad health problems, including mental retardation, congenital malformations, and behavioral abnormalities.
Building on a technique that uses a flourescent dye to "light up" pieces of human DNA, scientists at Lawrence Livermore National Laboratory in Livermore, Calif., can now quickly and reliably illuminate these extra chromosomes and thus identify men at risk for conceiving children with health problems. The new technique was developed to track malformations in chromosomes as cells divide. But researchers hope that the ability to pinpoint the presence of extra chromosomes in sperm will give them a tool to study external factors, such as smoking or exposure to drugs, that could cause mutations. "Now we can determine whether those things we worry about are really the problem," says medical biophysicist Andrew J. Wyrobek at Lawrence Livermore. Ultimately, the technique may make it possible to screen men for abnormal sperm cells.