Comparative Genome Analysis of the Primary Sex-Determining Locus in Salmonid Fishes

Abstract

We compared the Y-chromosome linkage maps for four salmonid species (Arctic charr, Salvelinus alpinus; Atlantic salmon, Salmo salar; brown trout, Salmo trutta; and rainbow trout, Oncorhynchus mykiss) and a putative Y-linked marker from lake trout (Salvelinus namaycush). These species represent the three major genera within the subfamily Salmoninae of the Salmonidae. The data clearly demonstrate that different Y-chromosomes have evolved in each of the species. Arrangements of markers proximal to the sex-determining locus are preserved on homologous, but different, autosomal linkage groups across the four species studied in detail. This indicates that a small region of DNA has been involved in the rearrangement of the sex-determining region. Placement of the sex-determining region appears telomeric in brown trout, Atlantic salmon, and Arctic charr, whereas an intercalary location for SEX may exist in rainbow trout. Three hypotheses are proposed to account for the relocation: translocation of a small chromosome arm; transposition of the sex-determining gene; or differential activation of a primary sex-determining gene region among the species

QTL for body weight and condition factor in Atlantic salmon (Salmo salar): comparative analysis with rainbow trout (Oncorhynchus mykiss) and Arctic charr (Salvelinus alpinus)

“…Ssa202DU is tightly linked to the sex-determining locus (approx. 4 cM) on the Atlantic salmon linkage map (Woram et al, 2003) and paternal allelic segregation at Ssa202DU was assumed to result in a reasonable estimation of progeny sex type. Using allelic segregation at a sex-linked marker cannot identify males versus females, but puts fish into two categories that correspond to different sexes.…”

“…Linkage maps have been developed for several salmonid fishes, including rainbow trout (RT; Oncorhynchus mykiss) (Young et al, 1998;Sakamoto et al, 2000;Nichols et al, 2003), Arctic charr (AC; Salvelinus alpinus) (Woram et al, 2004), and Atlantic salmon (Salmo salar) (Gilbey et al, 2004;Moen et al, 2004). Despite the extensive karyotypic rearrangements within the tetraploid salmonids (Hartley, 1987;Phillips and Rab, 2001) since their evolution from a diploid ancestor 25-100 MYA (Allendorf and Thorgaard, 1984), microsatellite markers have been able to identify chromosomal regions that are homologous across species (Woram et al, 2003).…”

Particularities of reproduction and oogenesis in teleost fish compared to mammals

“…Recent data actually confirm that sex chromosomes of O. niloticus, although identified by in situ hybridation techniques, are still weakly differentiated [12,13], and that sex determining genes can be localised on other chromosomes [14]. In salmonids, where the male is generally considered as the heterogametic sex, the determining locus can be situated on different chromosomes depending on the species [15], and other loci can also play a role [16]. Such weak differentiation of sex chromosomes may probably explain that viable abnormal new genotypes YY can be obtained relatively easily through various procedures, such as autofertilisation in hermaphroditic rainbow trout obtained by estrogenic treatment [17].…”

Heritable artificial sex chromosomes in the medaka, Oryzias latipes

“…Recent studies have shown that the sex chromosomes in two medaka-related species, O. luzonensis and O. dancena, are homologous to different autosomes in medaka Tanaka et al, 2007). Similar phenomena have been observed in salmonids and sticklebacks, suggesting that sex chromosomes have changed frequently in fish (Woram et al, 2003;Peichel et al, 2004;Phillips et al, 2007). In the Japanese frog, Rana rugosa, two distinct sex chromosome types, XX/ XY and ZZ/ZW, were observed in the same species (Miura et al, 1998).…”

“…Many species of fish and amphibians, including medaka, have homomorphic sex chromosomes. Recently, several comparative studies have provided evidence that different sex chromosomes and sex-determining systems have evolved in closely related fish species (Woram et al, 2003;Peichel et al, 2004;Takehana et al, 2007) and in the same species of frog (Ogata et al, 2003). The present results show that in vertebrates possessing homomorphic sex chromosomes, autosomes can easily become sex chromosomes.…”