Demonstration of specific heterochromatic segments in the orangutan (Pongo pygmaeus) by a distamycin/DAPI double staining technique.

Orangutan metaphase chromosomes, obtained from a female animal with trisomy 22, were stained by a recently developed distamycin/DAPI fluorescent technique which had been shown to differentiate specific C-bands on human chromosomes, as well as by other banding techniques. Distamycin/DAPI-brilliant fluorescence was observed in the short arm regions of acrocentric chromosomes 11--17, 22 and 23, and a brightly fluorescent paracentromeric band was seen on chromosome 8. A smaller amount of fluorescence was found adjacent to the centromere of most of the other chromosomes. Sequential distamycin/DAPI and Giemsa C-staining of the metaphases revealed that the "hot-spots" on acrocentrics correspond to C-band material in their short arm. The less intensely fluorescent centric bands on other chromosomes coincide with centromeric C-bands. Reverse fluorescent staining of organutan chromosomes with chromomycin A3 revealed brightly fluorescent regions at short arms of some acrocentrics probably confined to the satellite, either in a heteromorphic form (Nos. 11, 14, 17) or of similar size (No. 22).