Does differential selection on the 5S rDNA explain why the rainbow trout sex chromosome heteromorphism is not linked to the SEX locus?

Cytogenetic and Genome Research
Ruth B PhillipsGary H Thorgaard

Abstract

Many but not all rainbow trout strains have morphologically distinguishable sex chromosomes. In these strains, the short arm of the X has multiple copies of 5S rDNA and a bright DAPI band near the centromere, both of which are missing from the Y chromosome, which has a very small short arm. We examined the presence of these markers using fluorescence in situ hybridization (FISH) in four different YY clonal lines derived from different strains and compared the results with sexed fish of the Donaldson strain with the normal X/Y heteromorphism. The Y chromosome in two of the YY clonal lines (Arlee and Swanson) is indistinguishable from the X chromosome and it is positive for 5S rDNA and the DAPI bright band. On the other hand, both 5S rDNA sequences and the DAPI band were not found on the Y chromosome in Hot Creek and Clearwater which have the normal Y. Thus the presence of these two cytogenetic markers may account for the size difference between the short arm of the X and Y chromosome found in most rainbow trout strains. In fishes the expression of one type of 5S rRNA is restricted to oocytes and previous work suggests that although XX males are fairly common, XY females are rare, implying a selective disadvantage for XY females....Continue Reading

Citations

Dec 11, 2008·Proceedings of the National Academy of Sciences of the United States of America·Kim H BrownJames J Nagler
Sep 12, 2009·Animal Genetics·R B PhillipsG H Thorgaard
May 15, 2013·International Journal of Genomics·Ruth B PhillipsGary H Thorgaard

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