Thirteen (GT ) and four (CT ), microsatellite loci (n = 10 or more and n =20 or more, respectively) have been isolated from a partial genomic library of brown trout and sequenced. On average, a (GT ) repeat sequence occurs approximately every 23 kb and a (CT ) repeat sequence every 76 kb in brown trout genome. Primers for DNA amplifications using the polymerase chain reaction (PCR) were synthesized for three single locus microsatellites. Mendelian inheritance of the observed polymorphisms was confirmed in full-sib families. Four brown trout populations (10 unrelated individuals per population) were screened for polymorphism with these three microsatellite loci. The total number of alleles detected in the four populations is five at one locus, six at the other two microsatellite loci and is three, on average, per population. Heterozygosities range from 0.18 to 0.74. The largest differences in allelic frequencies occurred between the Mediterranean and the Atlantic populations: this result is congruent with previous allozymic data. The gene-centromere distances of the three microsatellite markers were determined on gynogenetic lines: post-reduction rates range from 0.17 to 0.60. For all the three microsatellite loci, the primers designed from brown trout sequences can be used in another closely related species of salmonid, the rainbow trout (Oncorhynchus mykiss). This last aspect supports the view that microsatellite markers may have wide application in genetic studies in salmonid species and fishes in general.

We report on the construction of a linkage map for brown trout (Salmo trutta) and its comparison with those of other tetraploid-derivative fish in the family Salmonidae, including Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and Arctic char (Salvelinus alpinus). Overall, we identified 37 linkage groups (2n ¼ 80) from the analysis of 288 microsatellite polymorphisms, 13 allozyme markers, and phenotypic sex in four backcross families. Additionally, we used gene-centromere analysis to approximate the position of the centromere for 20 linkage groups and thus relate linkage arrangements to the physical morphology of chromosomes. Sex-specific maps derived from multiple parents were estimated to cover 346.4 and 912.5 cM of the male and female genomes, respectively. As previously observed in other salmonids, recombination rates showed large sex differences (average female-to-male ratio was 6.4), with male crossovers generally localized toward the distal end of linkage groups. Putative homeologous regions inherited from the salmonid tetraploid ancestor were identified for 10 pairs of linkage groups, including five chromosomes showing evidence of residual tetrasomy (pseudolinkage). Map alignments with orthologous regions in Atlantic salmon, rainbow trout, and Arctic char also revealed extensive conservation of syntenic blocks across species, which was generally consistent with chromosome divergence through Robertsonian translocations.

Background: The development of large genomic resources has become a prerequisite to elucidate the wide-scale evolution of genomes and the molecular basis of complex traits. Linkage maps represent a first level of integration and utilization of such resources and the primary framework for molecular analyses of quantitative traits. Previously published linkage maps have already outlined the main peculiarities of the rainbow trout meiosis and a correspondance between linkage groups and chromosome arms has been recently established using fluorescent in situ hybridization. The number of chromosome arms which were covered by these maps remained unknown.

SummaryThe genetic variability of 7 fish-farm strains and 14 wild populations of brown trout was studied by electrophoretic analysis of 23 enzyme systems coded for by 52

First generation tetraploids were produced by hydrostatic pressure treatment before the first cleavage and raised until the adult stage. Their survival and growth were severely depressed when compared to the diploid control: after two years, no ovulated females were found although males produced sperm at 1 and 2 years of age and were mated individually with diploid females. The progenies were consistently normal with high survival rates. They were found to be almost all triploids by karyology, which failed to detect a significant rate of aneuploidies. However, the fertilizing ability of tetraploid males was always low (0 to 97% of the control; average 40%). Several arguments presented here support the hypothesis that diploid spermatozoas, which are wider than haploid ones, would be frequently blocked during their penetration through the micropyle canal. Second generation tetraploids were produced after such matings by heat shocks, causing the retention of the second polar body. Their survival and growth were much more satisfactory than in the first generation, although still lower than in diploid and triploid controls issuing from diploid parents. Performances of second generation triploids were comparable to those of diploids, and slightly better than those of conventional triploids issuing from diploid parents. 94.5% of the second generation tetraploids were male.