Rainbow Trout (Oncorhynchus mykiss) of Idaho and Alaskan Origin (2n = 58) Share a Chromosome Fusion Relative to Trout of California Origin (2n = 60)

Fluorescence in situ hybridization (FISH) was used to identify which chromosome pairs are involved in the difference in karyotypes of three clonal lines of Rainbow Trout (Oncorhynchus mykiss): OSU with 2n = 60, Clearwater with 2n = 58, and Swanson with 2n = 58. These lines appear to have karyotypes typical of strains from the regions from which they were derived (California, Idaho, and Alaska, respectively). Bacterial artificial chromosome clones containing mapped markers specific for different acrocentric pairs in the OSU strain were hybridized to chromosomes of hybrid fish. The OSU × Clearwater and OSU × Swanson hybrids have 2n = 59 with a chromosome pair consisting of one metacentric (fusion) chromosome and two acrocentrics. Both strains have the same chromosome fusion involving acrocentric chromosomes 25 and 29 of the OSU strain although they are from widely separate geographic regions. These results suggest that all of the 2n = 58 Rainbow Trout may have the same karyotype and a common origin.

Fig. 1.

(A) Chromosomes of the OSU × Clearwater hybrid hybridized with two probes (shown in white): a BAC clone containing the TCRbeta locus (telomeric on an acrocentric and a metacentric) and a random BAC G9 which hybridizes adjacent to the centromere on a metacentric and small acrocentric. (B) Chromosomes of the OSU × Swanson hybrid hybridized with two probes (shown in white): a BAC clone containing the TCRbeta locus (telomeric on an acrocentric and a metacentric) and a random BAC G9 which hybridizes adjacent to the centromere on a metacentric and small acrocentric. Chromosomes of the OSU strain hybridized with two probes (shown in white) to (C) TCRbeta and to (D) G9. The TCRbeta probe hybridized to the telomere of chromosome pair 25 and the G9 probe hybridized to a location adjacent to the centromere on chromosome pair 29

Contributor Notes

(RBP, MRM) Department of Biological Sciences, Washington State University Vancouver, 14204 NE Salmon Creek Ave., Vancouver, Washington 98686–9600; and (GHT, PAW) Department of Biological Sciences, Washington State University, P.O. Box 644236, Pullman, Washington 99164–4236. (RBP): phllipsr@vancouver.wsu.edu Send reprint requests to RBP.