General Considerations on the Karyotypic Evolution of Chelonia from the Amazon Region of Brazil

Abstract

The karyotypes of three species of Chelonia of family Chelidae, from the Amazon Region of Brazil are described: Platemys platicephala, with 2n=64; Mesoclemmys gibba, whith 2n=60 and Chelus fimbriatus with 2n=50. A comparison of cyto-genetics data is made with data of other species of Chelonia. It is suggested that centric fusions or elimination of microchromosomes, or both, are an important mechanism responsible for the karyotypic evolution of Chelonia. No sex chromosome is detected in the species here studied. In male meiosis of Chelus fimbriatus, the pachytene cells showed a bivalent with a defined region lacking pairing. This defferential behavior may be taken as an indication of sexual difference.