Chromosome indices in Indians.

Metaphase chromosomes from leukocyte cultures of Indian subjects have been measured. Mean length index and arm ratios compare well with figures from other parts of the world-except chromosome No. 2 which in a large percentage of cases is longer than Ch: No. 1. The fallacies involved in measuring and basing correlations on these are discussed. Introduction The characteristics of the normal human karyotype are now well established and it is an accepted fact that there is very little difference between karyotypes of different races. What then is our purpose in studying the Indian karyotype? To the best of our know ledge normal Indian karyotype has not been studied. Even a random sampling is not available. Perhaps the reason for this is that over the past couple of years only, there has appeared the beginning of an awareness of the importance of this field to medicine and research, perhaps too, to the sophisticated apparatus and technique required and the paucity of interested investigators. Since chromosome analysis is done in this loboratory as a research project, we felt that a survey of the Indian population to obtain their indices, though time consuming, could well be a worthwhile contribution to literature that already exists on the subject for the European peoples. Hence, the fact that no new con tribution can be made to karyotype in general, cannot detract from the usefulness of the project. As the data is factual the basis of this work will be comparison of a set of measurement from Indians with those of different races, published by others. Material and methods A microtechnique modified from Arakaki and Sparkes (1963) was used for culturing leucocytes from whole blood. Phytohaemagglutinin, (Wellcome), was used as mitogenic agent. Mitotic arrest was achieved with colchicine at a final concentration of 0.5ƒÊg/ml for a period of 2 hours only. Prewarmed 0.7% sodium citrate solution was used for hypotonic treatment. Cells in suspension were fixed in 1:3 acetic/alcohol, slides were flame dried and stained in 4% Giemsa's for 20 minutes. Technically perfect spreads with no overlap and straight chromosomes were selected and photographed under oil on 35mm. high contrast copy film. All negatives were enlarged to the same degree giving a final magnification of about 5000•~. Complete karyograms, by the unaided eye, were made fol lowing the Denver classification. Chromosomes were measured with dividers whose arms were locked to maintain a distance of 2mm. Another divider locked at 1mm was used at places of sligt curvature. The arms of each chromatid were measured from the exact centre of the centromere. The average of both chromatids was taken as the final measurement for each chromosome. From these figures the length index and arm ratios for each of the 46 chromosomes was calculated. 1 Additional Professor 2 Assistant Professor 466 G. Sadasivan and L. N. Ebenezer Cytologia 33 Ten individuals of both sexes were used for the study. Eight of them had no clinical stigmata, one was a case of gonadoblastoma (gonocytoma III), one a case of retinitis pigmentosa.