The development of the Q-banding technique for identification of the 46 human chromosomes
The Q-banding technique was the first method developed for identification of all 46 human chromosomes. This work was performed at the end of 1960 as collaboration between the late Torbjörn Caspersson, head of the department of Cell Research and Genetics, Karolinska Institute, in Stockholm and myself, a scientific asssistent at the same department.
We wanted to study the structure of DNA with highly sensitive fluorescence dyes. The material chosen for our first experiments were plants, many of which have fewer and larger chromosomes than mammals.
More than 30 DNA binding fluorochromes were tested but faded after a few seconds of irradiation with UV light and the morphology of the biological structures became blurred. The best results were obtained with quinacrine mustard which was more stable and produced characteristic banding patterns.
The next step was the application of quinacrine mustard staining to human chromosomes which, however, gave so poor results that we could not distinguish individual structures. However, after contrast enhancement of photographs we detected in male nuclei the Y chromosome as a weakly fluorescent dot. From there to the first karyotype it was a long and painful struggle. Especially the centromeres of the acrocentric chromosomes and the polymorphic regions on chromosomes l, 3 and 9 were confusing.
From our work with plant material we remembered, that in Vicia faba often 2 chromosomes had shown identical banding patterns. Controlling this phenomenon in human chromosomes we understood that homologous chromosomes were identical with respect to distribution and fluorescent intensity of bands.This observation made possible to find the chromosome pairs and finally to arrange the first human karyotype.