Sensitive chromosome probes recently discovered by a University of Toronto geneticist will make it easier to detect certain types of genetic and prenatal diseases, as well as being used to determine paternity and provide forensic evidence in criminal Probes are short pieces of DNA which bind to, and actually pinpoint, particular sites on a chromosome. Because these new probes are actually repeated hundreds or thousands of time at a particular site, they are much more sensitive than previouslyavailable ones. Of the 23 pairs of human chromosomes, Dr. F.H. Willard has discovered repeated probes or markers for six plus the gender determining X and Y chromosomes. "What we're trying to decide now is whether to isolate probes for the other chromosomes, orwhether we should utilize the eight we have," he says. Dr. Willard is currently negotiating with an American company to develop prenatal diagnostic tests, which, because the current tests are time consuming andtechnically difficult to do, are restricted to women over 35 and those who have a family history of chromosomal abnormalities. Prenatal tests using Willard's probes would be much simpler and faster to perform and could be available to all pregnant women who wish to take advantage of the technology. Current prenatal testing involves growing fetal cells in vitro and examining them, over one or two months, to see if there are two copies of a particular chromosome, which is normal, or one or three, which is abnormal. A test using Willard's probes would require only a few cells and a few days to detect abnormalities. "I don't think it's beyond therealm of possibility that these kinds of tests could eventually be done by an obstetrician in the office during the early stages of pregnancy," he adds. The determination of gender is another possible use for the probes. Many diseases, such as Duschene's muscular dystrophy, show up on the X chromosome, manifesting only in boys. Willard thinks it is...
