A thermal denaturation study of genomic DNAs from North American minnows (Cyprinidae: Teleostei).

Base compositions and differential melting rate profiles of genomic DNAs from twenty species of North American cyprinid fishes were generated via thermal denaturation. Base pair composition expressed as % GC values ranged among the twenty species from 36.1-41.3%. This range is considerably broader than that observed at comparable taxonomic levels in other vertebrate groups. Both the range and average difference in base pair composition between species in the diverse and rapidly evolving genus Notropis were considerably greater than those between species in other North American cyprinid genera. This may indicate that genomic changes at the level of base pair composition are frequent and possibly important events in cyprinid evolution. Compositional heterogeneity and asymmetry values among the twenty species were uniform and low, respectively, suggesting that most of the species lacked DNA components in their genomes which differed substantially from their main-band DNAs in base pair composition. The melting rate profiles revealed a prominent and distinct heavy or GC-rich DNA component in the genomes of three species belonging to the subgenus Cyprinella of Notropis. These and other data suggest that the heavy melting component may reflect a large, comparatively GC-rich family of highly repeated or satellite DNA sequences common to all three genomes.