Rana rugulosa, family Ranidae, are common amphibians which can be found in most regions of Thailand. The animals play very important role in the ecosystem. It is well known that they contribute tremendously on the food chain and have great influence on the environment surrounding the particular habitat. Moreover, the frogs can serve as the very good protein source for men. However, the sex chromosomes in this frog have not been identified. The studies on this animal's sex chromosomes are therefore not only interesting but also important since each species will exhibit different forms of the chromosomes. This study compared the karyotypes between males and females by using the conventional staining methods. It was found that the number of sex chromosomes in both males and females was similar namely 2n = 26. Five pairs of large chromosomes were classified as follows: four pairs as metacentric-type and the other as submetacentric-type. On the other hand, the results on the chromosomes were as follows 4 of theeight pairs were metacentric and the other 4 were submetacentric. Moreover, secondary constriction was found on the long arm of the eight in both male and female chromosomes. When the G-band and C-band stainings were conducted in order to indicate the position of the nucleolar organizer regions and also to check on the type of self replication, it was found that 13 pairs of the chromosomes are homomorphic since no difference in each pair of chromosomes were obviously detectable between these male and female frogs. From these results, it could be concluded that the sex chromosomes in Rana rugulosa have not yet evolutionarily developed.
