Repetitive DNA and Feulgen hydrolysis kinetics in three species of Bufo

Two North American species of the genus Bufo (Bufo cognatus and Bufo boreas, 2n = 22) and one African species (Bufo regularis, 2n = 20) were analyzed with respect to their repetitive DNA fractions and the behaviour of their chromatin to the acid hydrolysis at different times. The mean melting point of the total isolated DNA decreased from 89 degrees C to 87 degrees C with a genome size increase from 4.4 to 7.5 pg. The differences in genome size can only partly be explained on the basis of repetitive DNA fractions (renaturing up to Cot 10 in 0.12 M phosphate buffer). Several fractions in this repetitive range behave independently in the three species and the spectrum of repetitive fractions in the African Bufo regularis differs distinctly from those of the American toads. When fixed chromatin of these species in histochemical preparations is hydrolyzed with 5N HCl during the Feulgen reaction, the kinetics of depurination are equal in all species, while hydrolytic DNA breakdown proceeds distinctly more slowly in Bufo reularis as compared to the other species.