Delineation of human chromosome contour by heat treatment and hematoxylin staining

An unusual form of staining was observed as a result of heat treatment: chromosome contour became easily recognizable. Chromosome contour is optimally delineated by heat treatment of metaphase preparations in 0.06 M phosphate buffer, pH 6.8–7.0 at 95° C for 10 min, and subsequent staining with Heidenhain's hematoxylin. This result is obtained by a process similar to that in which Giemsa has been reported to stain particular foci considered to represent selective staining of constitutive heterochromatin. Mordanting with 3% ferrous ammonium sulfate produced maximum staining. However, hematoxylin (Harris) also stained the periphery of chromosomes. A transitional temperature existed between 70° C and 80° C in which contour became evident. When metaphase preparations were heated at 90–95° C, contour occurred on some chromosomes within 3 min and was demonstrated in 100% of the chromosomes analysed after 10 min of heat treatment.Supported in part by a grant to C. Romero-Sierra from the Defence Research Board of Canada (DRB 9350-24) and to E. A. MacKinnon from the Medical Research Council of Canada (MA-4135).