ABNORMALITIES OF MEIOSES IN MALE RECIPROCAL HYBRIDS BETWEEN THE HIROSHIMA AND ICHINOSEKI POPULATIONS OF RANA-JAPONICA

In order to elucidate cytogenetically the cause of male sterility in i ntraspecific hybrids of Rana japonica, the behavior of chromosomes in the first meiosis was observed in spermatocytes from male reciprocal h ybrids between two populations from Hiroshima and Ichinoseki. In the p arental Hiroshima and Ichioseki populations, 2530 (96.7%) meiotic spre ads had 13 bivalents and 78 (3.0%) contained 12 bivalents and two univ alents, whereas in reciprocal hybrids only 337 (7.0%) contained 13 biv alents and the other 4445 (93.0%) had 2-26 univalents. A total of 3164 7 (93.4%) bivalents was ring-shaped and the other 2234 (6.6%) were rod -shaped in both parental populations, whereas in reciprocal hybrids 26 352 (57.1%) and 19819 (42.9%) bivalents were ring- and rod-shaped, res pectively. These results show that meiotic chromosomes of reciprocal h ybrids are characterized by a remarkable increase in univalents and ro d-shaped bivalents.