Abstract
Trypsin G-banding of chromosomes from North American cyprinid fishes was used to address phylogenetic problems within the group and to demonstrate the occurrence of G-bands which are not differentially rich in AT DNA base pairs. G-band homology of the long arm of the F', C', and E' NOR chromosomes found among six North American cyprinid species, in concert with a hypothesis of species relationships based on morphology, suggests that a NOR situated terminally on the largest chromosome in the complement may represent the plesio-morphic NOR character state within the large “Notropis”-like shiner assemblage. Outgroup comparison suggests that this chromosome may also represent a synapomorphy for the same lineage. Evidence exists which suggests that the F' NOR is ancestral and that the C' and E' NORs are derived. The occurrence in cyprinids of trypsin-induced G-bands which are not differentially rich in AT-/GC-DNA base pairs may indicate that the evolution of trypsin-induced G-bands preceded the evolution of differential AT-/GC-richness. The use of trypsin G-banding in cyprinids in expected to permit the identification of previously cryptic chromosomal rearrangements both within and among species.
