IN-SITU HYBRIDIZATION APPROACH AT INFRAGENIC LEVEL ON METAPHASE CHROMOSOMES

Analysis of the retinoblastoma locus (RB1) by in situ hybridization at the infragenic level was done using human chromosomes. A high level o f resolution was attained with nonisotopic in situ hybridization on ba nded chromosomes in both fluorescence and electron microscopy. DNA seq uences less than 100 kb apart could be positioned on band 13q14 in the order expected from molecular mapping. These observations suggest tha t the DNA target of hybridized probes on metaphase chromosomes may cor respond to nucleoprotein loops giving a resolution comparable to that obtained in interphase nuclei.