A DNA probe suitable for the detection of chromosome 21 copy number in human interphase nuclei by fluorescence in situ hybridization

Objective To prepare DNA probe which can be used to accurately detect chromosome 21 copy number in human interphase nuclei by fluorescence in situ hybridization (FISH). Methods A probe was produced by universal primer PCR from YAC clone 881D2 and characterized by FISH to metaphases and interphase nuclei of peripheral lymphocytes from 8 normal individuals and 5 patients suffering from trisomy 21. Results A DNA probe was produced and its characteristics were: (1) Most of the probes ranged in size from 350bp to 750bp; (2) The hybridization signals of the probes were located near centromere on long arm of human chromosome 21; (3) In 1524 metaphases scored, about 99. 95% of hybridization signals were located on chromosome 21; (4) The signals were very bright and recognizable easily in both metaphases and interphases nuclei; (5) The expected copy number of chromosome 21 was detected by FISH with the probe in more than 98.40% of interphase nuclei and 99.60% of metaphases. Conclusion The DNA probe reported here is suitable for the detection of chromosome 21 copy number in interphase nuclei and for the study of segregation of chromosome 21 during mitosis of human lymphocytes in culture.