Genetic mapping of Y-chromosomal DNA markers in Pacific salmon.
Sex chromosomes in fish provide an intriguing view of how sex-determination mechanisms evolve in vertebrates. Many fish species with single-factor sex-determination systems do not have cytogenetically-distinguishable sex chromosomes, suggesting that few sex-specific sequences or chromosomal rearrangements are present and that sex-chromosome evolution is thus at an early stage. We describe experiments examining the linkage arrangement of a Y-chromosomal GH pseudogene (GH-Y) sequence in four species of salmon (chum, Oncorhynchus keta; pink, O. gorbuscha; coho, O. kisutch; chinook, O. tshawytscha). Phylogenetic analysis indicates that GH-Y arose early in Oncorhynchus evolution, after this genus had diverged from Salmo and Salvelinus. However, GH-Y has not been detected in some Oncorhynchus species (O. nerka, O. mykiss and O. clarki), consistent with this locus being deleted in some lineages. GH-Y is tightly linked genetically to the sex-determination locus on the Y chromosome and, in chinook salmon, to another Y-linked DNA marker OtY1. GH-Y is derived from an ancestral GH2 gene, but this latter functional GH locus is autosomal or pseudoautosomal. YY chinook salmon are viable and fertile, indicating the Y chromosome is not deficient of vital genetic functions present on the X chromosome, consistent with sex chromosomes that are in an early stage of divergence.
Devlin
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RH
Fisheries and Oceans Canada, West Vancouver, BC, Canada. devlinr@dfo-mpo.gc.ca
Biagi
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CA
Smailus
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D000818:Animals; D001483:Base Sequence; D015139:Blotting, Southern; D002874:Chromosome Mapping; D005260:Female; D005819:Genetic Markers; D008297:Male; D012474:Salmon / Q000235:genetics*; D012689:Sequence Homology, Nucleic Acid; D019849:Sex Determination Processes; D013045:Species Specificity; D014998:Y Chromosome
D005819:Genetic Markers