Preimplantation genetic diagnosis. In situ hybridization as a tool for analysis.

In situ hybridization allows one to directly visualize DNA sequences of interest for which probes are available. Fluorescent signals can be detected in single cells in either metaphase or interphase nuclei, thus obviating the need for cell synchronization. The potential to use this technology in conjunction with in vitro fertilization techniques to genetically analyze an embryo before transfer could offer patients at genetic risk an alternative. Currently, these patients wait until 9 to 16 weeks' gestation to find out about the genetic makeup of their pregnancy. As such, sexing the embryos of patients at risk for transmitting sex-linked disorders or for performing numerical chromosome analysis could be performed before embryo transfer. Techniques for applying in situ hybridization to single cells obtained from embryos are presented. Hybridization of specific probes to blastomeres of mouse and human embryos as well as sperm is demonstrated.