Complex sentence: While radioisotope-labeled probes had been hybridized with DNA since 1969 movement was now made in using fluorescently labeled probes, and hybridizing them to chromosomes preparations made using existing techniques, this technique is called "fluorescent in situ hybridization" (FISH).
Split into simpler sentences: While radioisotope-labeled probes had been hybridized with DNA since 1969, movement was now made in using fluorescently labeled probes. Hybridizing them to chromosomes preparations made using existing techniques came to be known as "fluorescent in situ hybridization" (FISH).