Variation of Y-chromosome DNA markers in Chinook salmon (Oncorhynchus tshawytscha) populations

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Abstract
Two Y-chromosome DNA markers (a repetitive sequence, OtY1, and a single-copy marker, GH-Y) tightly linked to the sex-determination locus have been examined for their association with sexual development among 55 populations of Chinook salmon (Oncorhynchus tshawytscha) from the Yukon, British Columbia, Washington, Oregon, and Idaho. Normal linkage has been observed in 96.7% of 2478 individuals examined. Only five males (0.44%) were found lacking both markers (none from Canadian systems), and 14 females (1.04%) from US populations and two females (0.15%) from Canadian populations were found to possess both markers. Variants identified included weakly amplifying alleles for GH-Y and OtY1 and structural variants identified by Southern-blot analysis. The frequency of variants in males was more than 2-fold that in females, and males deficient in GH-Y were more common (3.6%) than males deficient in the repetitive OtY1 sequence (0.7%). Some individuals (of both sexes) possessed fewer copies of the OtY1 repeat than normal males, revealing molecular dynamics that alter Y-chromosome structure within and among populations. A population (Hanford Reach) previously reported as having a high incidence of females possessing the OtY1 marker, and suspected of being sex-reversed, was found to have normal sex-marker genotypes in the present study.
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