Isolation of a Y-Chromosomal DNA Probe Capable of Determining Genetic Sex in Chinook Salmon (Oncorhynchus tshawytscha)

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Abstract
We have used subtractive hybridization methodologies to selectively clone a DNA fragment from the Y chromosome of chinook salmon (Oncorhynchus tshawytscha). This clone specifically detects a single 8-kb Bam HI restriction fragment in Southern blots of male genomic DNA that is absent in females. This sex-specific pattern was observed in over 50 individuals from five separate chinook stocks, suggesting that the organization of this sequence is conserved in this species. The strength of the hybridization signal, and the pattern observed in multiple enzyme digests, indicates that this sequence is repeated in the male chinook genome. With long autoradiographic exposures, fainter additional sequences can also be detected both in males and females, suggesting that other similar sequences not organized in a sex-specific fashion are found on the X chromosome and/or autosomes. Examination of the segregation of this DNA sequence in families showed that the male-specific pattern segregates from father to son, providing strong evidence that the DNA probe is from the Y chromosome. The application of Y-chromosomal probes to the commercial culture of this species will simplify the synthesis of new monosex strains and allow verification of existing genotypic female, phenotypic male stocks.
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