HETEROMORPHIC SEX-CHROMOSOMES IN THE AUSTRALIAN FROG CRINIA-BILINGUA (ANURA, MYOBATRACHIDAE)

The karyotype of Crinia bilingua was examined and analysed with standard staining, C-banding, and silver-staining. Heteromorphic sex chromosomes of the ZW female/ZZ male type were observed. The larger W chromosome is submetacentric and the smaller Z chromosome is acrocentric. The centromere and proximal region of the short arm of the W chromosome consist of constitutive heterochromatin (C-band region), and beyond this is a small euchromatic terminal region. The centromere of the Z chromosome did not C-band. The long arms of the Z and W chromosomes are euchromatic and equal in length. The nucleolar organiser region occurs terminally on the long arm of both the Z and W chromosomes, and there is no cytological evidence for inactivity of the nucleolar organiser region on the W chromosome. These features indicate an early stage in the evolution of heteromorphic sex chromosomes.