Mutation Research, 126 (1984) 81-92 81 Elsevier MTR 03826 Diagrammatic representation for chromosomal mutagenesis studies I. Karyotypes most similar to that of man B. Dutrillaux, Martine Muleris and Mafia Paravatou-Petsota ER No. 264, CNRS, Institut Curie, Section de Biologie, 26, rue d'UIm, 75231 Paris Cddex 05 (France) and Centre d'Etudes Nucldaire, Laboratoire de Mutagenbse; Ddparternent de Protection (Service de Pathologie Expdrirnentale), B.P. No. 6, 92260 Fontenay-aux -Roses (France) (Received 10 March 1983) (Revision received 13 October 1983) (Accepted 17 October 1983) Summary In an attempt to discover which primate species have the karyotypes most similar to that of man, the chromosome numbers, the Nombre Fondamental and the numbers of chromosomal rearrangements separating the karyotypes of many species were considered. In addition to man, 6 species were selected for their karyotypic similarities and 1 for its dissimilarity. A model representing the karyotypes, by 2 diagrams, is proposed for these 8 species. These diagrams characterize each karyotype, as well as the theoretical random distribution of break-points, after the effect of a clastogenic agent. This allows one to make quantitative analyses of any type of chromosomal rearrangement, with objective criteria, and should improve the study of chromosomal mutagenesis, and particularly interspecies comparisons. Chromosomal rearrangements are frequently considered to be indicators of the effects of muta- gens. Concerning ionizing radiations, it is well known that a relationship exists between the ab- sorbed dose and the frequency of the rearrange- ments, but, for various reasons, and particularly because of their ease of detection, non-transmissi- ble rearrangements, such as dicentrics, are almost exclusively studied and quantified in standard conditions. Qualitative studies, regarding the location of break-points in various rearrangements, appear much less frequently, probably because they are more difficult, and require careful analysis with chromosome banding. The major difficulty in these studies lies, however, in the lack of systematization in the interpretation of the results. An analysis is thus limited, producing only vague considerations, such as the possible existence of hot spots. This difficulty is aggravated if the results have to be extrapolated from one species to another, as dur- ing evolution, many chromosomal rearrangements have modified the karyotypes and thus the char- acteristics of the chromosomes. It would, there- fore, be useful to fix the characteristics of the karyotype of any species under study, which would allow an analysis of the rearrangements in relation to these characteristics, before attempting to ex- trapolate the results to any other species, and in particular to our own. Our aim is first of all to compare the karyo- types of many primate species with the classical numerical and morphological criteria, as well as with their phylogenetical relationships in order to find the karyotypes most similar to that of man. Secondly, the karyotypes of the selected species 0027-5107/84/$03.00 © 1984 Elsevier Science Publishers B.V.