Chromosomal heterochromatin differentiation in North American cyprinid fishes.

Abstract

Chromosomal heterochromatin was differentiated in two closely related spe-cies of the North American cyprinid genus Notropis. The amounts of heterochro-matin in the genomes of the two species were appreciable: 35% in N. lutrensis and 39% in N. venustus. The chromosomal distribution of heterochromatin was similar in both species: most or all chromosomes contained procentric bands, a few pos-sessed terminal and/or interstitial bands, and there was a preponderance of sub-metacentric and acrocentric chromosomes with entirely heterochromatic short arms. Several chromosomes could be putatively homologized either within or between the two species, although in general the amount and type of heterochromatin made precise homologization difficult. The total amount of heterochromatin resolved in these two species is considerably more than that found among most of the relatively few fish species studied to date. Heterochromatin appears to be one of the few potentially variable fractions of the cyprinid genome which may have contributed to the extensive speciation exhibited by these fish in North America. A few marker chromosomes, specifically the one bearing the nucleolus organizer region or NOR, may prove valuable in cyprinid taxonomy.