MARKER CHROMOSOME IDENTIFICATION BY MICRO-FISH

Micro-FISH was used to elucidate the chromosomal origin of marker chro mosomes in three patients. Ten copies of marker chromosomes were colle cted with microneedles from GTG banded metaphases, transferred to a co llecting drop and amplified by means of DOP-PCR. The PCR products were labeled with biotin-l4-dATP and used as FISH probes for hybridization to normal metaphase chromosomes and to metaphase chromosomes of the p atients (reverse painting). With the generation of chromosome region-s pecific painting probes by PCR amplification of microdissected DNA and subsequent FISH it was possible to identify the marker chromosomes in all patients. One marker appeared to be derived from the centromere r egion of the X-chromosome and the proximal third of the long arm, one from the centromere region of chromosome 17 and one marker chromosome was identified as an isochromosome 18p.