Chromosome banding in amphibia. XX. DNA replication patterns in Gastrotheca riobambae (Anura, Hylidae).

Replication banding patterns were induced in the chromosomes of Gastrotheca riobambae by treating cell cultures with 5-bromodeoxyuridine (BrdU) and deoxythymidine (dT). In particular, the time sequence of replication of the highly differentiated XY/XX sex chromosomes was meticulously analyzed throughout the S phase. In the homogametic female, BrdU/dT labeling revealed no evidence of asynchronous replication between euchromatic regions in the XX pair. Minor replication asynchronies between the two X chromosomes were restricted to the heterochromatic C-bands. These results are further proof that dosage compensation in Amphibia for X- or Z-linked genes does not occur by inactivation of one of the two (XX or ZZ) sex chromosomes in the cells of homogametic individuals. In the very large and almost completely heterochromatic Y chromosome of G. riobambae, the various C-bands comprise at least three different structural categories, resulting in a complex pattern of early- and late-replicating bands along the Y chromosome.