In the summer of 1989, one of us (SLG), along with his mentor, Dorothy Warb- ton, attended the Tenth International Workshop on Human Gene Mapping. The me- ing was held at Yale University in celebration of the first such event, which also took place there. This meeting was not open to the general public; one had to have contributed to mapping a gene to be permitted to attend. The posters, of course, were therefore all related to gene mapping, and many were covered with pretty, colorful pictures of a novel, fluorescent application of an old technology, in situ hybridization. Walking through the room, Dorothy remarked that, because of this new FISH technique, ch- mosomes, which had become yesterday’s news, were once again “back in style. ” Approximately three years later, a commercial genetics company launched a FISH assay for prenatal ploidy detection. A substantial number of cytogeneticists across the country reacted with a combination of outrage and panic. Many were concerned that physicians would be quick to adopt this newfangled upstart test and put us all on the unemployment line. They did not at the time realize what Dorothy instinctively already knew—that FISH would not spell the doom of the cytogenetics laboratory, but it would, rather, take it to new heights.