Three Sex Loci and An sdY In Tasmanian Atlantic Salmon

Although Atlantic salmon sex is determined by a genetic male heterogametic sex determining system, sex reversal can be accomplished via hormonal treatment. In Australia where males are unmarketable due to environmental related problems, sex reversed females (neo-males) are crossed with normal females to produce all female harvest stock.  However, neo-males are difficult to distinguish from males and this makes early culling of males difficult.  Therefore, a sex specific genetic marker was needed to distinguish neo-males from true males.  Previously, through microsatellite and SNP sex linked markers, we identified three sex-determining loci in Tasmanian Atlantic salmon, on chromosomes two, three and six respectively.  An exon based PCR test for the rainbow trout master sex determining gene (sdY) was consistent as a male specific marker across parents of 47 families and all three sex linked loci.  However, in the offspring, consistency between sdY presence/absence and phenotypic sex dropped to 543/555 for males and 369/384 for females.  Within the 912 consistent sdY phenotype predictions 27 did not agree with genotype.  Although it is possible that sdY has relocated whenever sex linked haplotype, sdY presence/ absence and sex phenotype do not agree, the most promising individuals (18) to test if sdY has relocated are phenotypic males in which sdY is present but the sex linked haplotype is female.   Analysis of the offspring of such individuals would be necessary to confirm relocation.