ALLOMETRY OF BASE-PAIR SPECIFIC-DNA CONTENTS IN TETRAPODA

Cells of 82 species of Tetrapoda were stained with DNA base pair speci fic fluorochromes (Hoechst 33258 and olivomycin) and studied by means of flow cytometry. The genome size range was about 50-fold. The class Amphibia, which had the widest range of genome size variation (about 2 0-fold), exhibited linear allometry in their base pair specific DNA co ntents (bps-C-values), i.e., the more DNA they had, the lower the quot ient of AT-pairs (C(AT) = 0. 1 3 + 0.87 X C(GC), r = + 0.998). Data fo r Mammalia, pooled with amphibians, fell on the same allometric line a t the lower extreme end of genome size range, supporting the correlati on. Reptilia-Aves (OT Reptilia alone) pooled with Amphibia did not con form with this relationship. Reptilia-Aves form their own line (zone), pooled with Mammalia, this group showed no regularities in the relati onship of their bps-DNA contents. Besides revealing the allometry of b ps-C-values, these data indicate an integral genomic feature, localiza tion within the same regression line, which Mammalia share with Amphib ia but not with recent Reptilia (and Aves). These data also suggest th at the relationship between DNA base frequencies and genome size is no nlinear (reciprocal); to obtain a linear relationship, the bps-C-value s should be used- It is also concluded that caution is needed when DNA -content is measured for comparative purposes using a fluorescent dye which is known to be base-pair specific. DNA content values obtained w ith fluorochromes with different specificity may differ as much as by a factor of 1.8, the average discrepancy level is about 14 %.