CHIASMA ANALYSES OF THE PARASITE FLUKES, SCHISTOSOMA AND PARAGONIMUS (TREMATODA), BY USING THE CHIASMA DISTRIBUTION GRAPH

Chiasma frequency and chiasma distribution pattern of three parasite f lukes, Schistosoma mansoni (n=8), S. japonicum (n=8), and Paragonimus ohirai (n=11) were investigated by using the chiasma distribution grap h. It was revealed that there is a minimum value of interference dista nce between two interstitial chiasmata in each bivalent (1.8% of the t otal bivalent length), but frequency distributions of interstitial chi asmata are random and almost uniform except the centromere and telomer e regions in which chiasma formation is suppressed. As no chiasma term inalization was detected, the so-called terminal chiasma were best int erpreted by an achiasmatic terminal association. resulting from the te lomere-nuclear membrane association. The mean chiasma frequency per ce ll estimated from interstitial chiasmata is 15.3 in S. mansoni and P. ohirai, but very low (3.0) in S. japonicum. A genetic mechanism contro lling the level of chiasma frequency was discussed with reference to t he results in mammals.