The Chromosomes of Man and the Great Apes. The Inference of Interspecific Homology

Abstract

Since the time when Tjio and Levan (1956) and Ford and Hamerton (1956) first reported that the normal chromosome number of man was 46, thus ending a long-standing controversy, substantial improvements in the methods of obtaining chromosome preparations have been made. These have permitted the study of other species, among which are included man’s closest living relatives, the great apes: Pan troglodytes, Pan paniscus, Gorilla gorilla and Pongo pygmaeus. Except for an early report of Yeager et al. (1940), who had observed meiotic divisions in preparations of the testis of a chimpanzee (Pan troglodytes), nothing was known about chromosome number in the great apes. Based on the number of observed bivalents, Yeager et al. (1940) had correctly reported the diploid chromosome number of this species to be 2n=48. Twenty years later, Young et al. (1960) confirmed these findings in the chimpanzee, using chromosome preparations obtained from bone marrow. Later on, the chromosomes of the other species of great ape were studied for the first time (Chiarelli, 1961; Hamerton et al., 1961; Chiarelli, 1962), and their diploid chromosome number was also found to be 48. The karyotypes of the great apes were compared to that of man as a first attempt to study the phylogeny of human chromosomes (Chu and Bender, 1962; Bender and Chu, 1963; Hamerton et al., 1963; Klinger et al., 1963; Egozcue, 1969).