INTERSPECIFIC CHROMOSOME HOMOLOGIES IN SALMONID FISHES IDENTIFIED USING PAINT PROBES

¹ Department of Biological Sciences, University of Wisconsin-Milwaukee, PO BOx 413, Milwaukee, WI 53201

² Cancer Genetics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, MD.

Whole-arm chromosome paint probes were produced for several rainbow trout (Oncorhynchus mykiss) chromosomes by microdissection. The probes were labeled with Spectrum Orange (Vysis) using the polymerase chain reaction and used in FISH (fluorescence in situ hybridization) experiments with rainbow trout, chinook salmon (Oncorhynchus tshawytscha), and lake trout (Salvelinus namaycush) chromosomes. Many of the probes highlighted only one chromosome pair, suggesting that the majority of the chromosome pairs in these ancestrally tetraploid fishes are diploidized. However one of the probes highlighted the telomeric region of a second (presumably homeologous) chromosome pair. This is consistent with genetic evidence that some duplicate loci near telomeres still share alleles. One of the rainbow trout paint probes prepared from an autosome paints the long arms of the lake trout sex chromosome pair and a paint probe previously made from the short arm of the lake trout Y chromosome paints half of the short arm of a rainbow trout autosome pair. These results are consistent with separate evolution of the sex chromosomes in Oncorhynchus and Salvelinus.