Chromosomes of the Chinese Hamster, Cricetulus griseus: I. The normal complement and identification of sex chromosomes

1. The normal complement of the Chinese hamster consists of 11 pairs of readily distinguishable chromosome types. 2. The sex bivalent of the Chinese hamster is the third largest in the complement. It resembles the J-shaped “isomorphic” Chromosome pair VIII. Earlier selections by Matthey and Pontecorvo, involving heteromorphism and or the largest metacentrics as sex elements, are considered incorrect on the basis of present experimental data. 3. Variation in the length of Chromosome I is due to mechanical stretching, leaving the impression of heteromorphism of homologues. 4. Reciprocal translocations are readily identified in offspring sired by x-irradiated males. The presence of a normal appearing sex bivalent with a ring or chain of four configuration, involving Matthey's “X” chromosome, support the writer's views that the largest metacentric pair is purely autosomal. 5. Experimental proof of the actual sex chromosomes remains to be demonstrated.