Abstract
Chromosome-number distributions in 5 species of Japanese snakes are presented in Table 1.
Elaphe climacophola, E. quadrivirgata and Natrix vibakari showed the same diploid number, 36, with an identical karyotype showing 8 pairs of macrochromosomes and 20 microchromosomes. Agkistrodon halys showed the same chromosome number, but had a slightly different karyotype explicable by pericentric inversion of the no. 6 macrochromosomes. Rhabdophis tigrinus had 40 chromosomes consisting of 8 pairs of macrochromosomes and 24 microchromosomes. Its karyotype seems to be explained by reciprocal translocation and centromeric fusion-fission mechanism in the four species.
Sexual dimorphism of the chromosomes is represented by the no. 4 (or 5) chromosomes with the ZZ/ZW mechanism, showing female heterogamety. The Z chromosome is metacentric, while the W subtelocentric. The morphological difference between them is interpreted as a result of pericentric inversion.
