Sex chromosome differentiation in the Japanese brown frog, Rana japonica. I.Sex-related heteromorphism of the distribution pattern of constitutive heterochromatin in chromosome no.4 of the Wakuya population

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To clarify the sex-related differences of chromosomes in the Japanese brown frog, Rana japonica, its chromosomes were analyzed by C- and late replication banding techniques. This species was characterized by ♂XY/♀XX sex chromosomes. There were three types (A, O and B) of chromosome No. 4 with respect to C-banding pattern. The type A had a C-band at the basal portion of the long arm, the type O had no such band, and the type B had double bands at the corresponding region. Almost all (97. 6%) of the females examined showed the AA type and 2. 4% the AO type, while 85. 7% of the males examined showed the AO type, 10. 7% the AA type, 1. 2% the OO type and 2. 4% the AB type. Histological examination of the testes of these AA, OO and AB males and the sex ratio of their offspring with AA females revealed that the OO and AB males were genetic XY males, while the AA males were composed of spontaneously sex-reversed XX females and genetic XY males. These results suggest that the genetic XY males of AA and the presumably genetic XX female of AO were produced by a recombination between the C-band in chromosome No. 4 and the site of a male-determining gene on the same chromosome. The OO male was probably produced from a mating of an XY male of AO with an XX female of AO.
1994-12-15