Cytogenetic studies in North American minnows (Cyprinidae) 26. Chromosomal NOR phenotypes of 21 species from the western United States

• Published in: Cytologia Vol. 57; no. 4; pp. 443 - 453
• Main Authors: Jenkin, J D, Li, Y C, Gold, J R
• Format: Journal Article
• Language: English
• Published: 01.01.1992
• Subjects: Cyprinidae; Freshwater; USA, West
• ISSN: 0011-4545

Karyotypes and chromosomal nucleolus organizer region or NOR phenotypes of 19 described and two undescribed species of western North American cyprinids are documented. All 21 species examined possessed 2N = 50 chromosomes and at least two pair of NOR-bearing chromosomes. The high incidence of multiple NOR chromosomes among western cyprinids is unusual. One pair of A NOR chromosomes was found in all 21 species, and 17 species possessed a second pair of A NOR chromosomes. An AA NOR state was hypothesized to represent a chromosomal synapomorphy uniting western cyprinids (including the genus Richardsonius ) into a monophyletic assemblage. Within this clade, a transition from an A NOR to a D NOR was hypothesized to represent a chromosomal synapomorphy uniting three species of the subgenus Gila , and an addition of an F NOR was hypothesized to represent a chromosomal synapomorphy uniting two species of the genus Rhinichthys . Chromosomal NORs in western cyprinids appear conserved relative to eastern cyprinids and may be the result of (i) a process of karyotypic canalization, and/or (ii) character state reversal in, or introgressive hybridization among, western cyprinid genera.