Alteration of the sex determining system resulting from structural change of the sex chromosomes in the frogRana rugosa

✍ Scribed by Ohtani, Hiromi; Miura, Ikuo; Hanada, Hideki; Ichikawa, Youko

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 617 KB
• Volume: 286
• Category: Article
• ISSN: 0022-104X
• DOI: 10.1002/(sici)1097-010x(20000215)286:3<313::aid-jez10>3.0.co;2-b

✦ Synopsis

Rana rugosa in Japan is divided into four geographical races on the basis of the karyotype of the sex chromosomes: one in which heteromorphic sex chromosomes occur in the female sex (ZW/ZZ-system), another in which they are present in males (XX/XY-system), and the remaining two in which no heteromorphism is seen in either sex. The last two inherit the XX/XY sex determining system. Y and Z chromosomes in the former two are of the same karyotype as the no. 7 chromosomes seen in one of the latter two, whereas X and W are caused by two inversions that occurred in the original Xs (no. 7). In this study, we first attempted to detect the structural difference between the resulting X and W by examining their chiasma formation. The chiasma distribution between X and W was closely similar to that between two Xs, suggesting that the W and X are identical in structure. Regarding the change from XX/XY-to ZW/ZZ-system, the simplest explanation is that the putative female-determining gene(s) on the W grew functionally stronger by inversions. Next, we examined the sex of triploids having two Xs and one Z. The data showed that the triploids with two original Xs and a Z were all male, whereas most of those with two resulting Xs and a Z developed into females as expected. We speculated that the femaledetermining gene(s) on the resulting X grew mildly stronger functionally by position effect, whereas those on the W grew much stronger for some other reason (e.g., duplication).