(CT)(N) AND (GT)(N) MICROSATELLITES - A NEW CLASS OF GENETIC-MARKERS FOR SALMO-TRUTTA L (BROWN TROUT)

Thirteen (GT)n and four (CT)n microsatellite loci (n = 10 or more and n = 20 or more, respectively). have been isolated from a partial genom ic library of brown trout and sequenced. On average, a (GT)n repeat se quence occurs approximately every 23 kb and a (CT)n repeat sequence ev ery 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 polymorph isms was confirmed in full-sib families. Four brown trout populations (10 unrelated individuals per population) were screened for polymorphi sm with these three microsatellite loci. The total number of alleles d etected in the four populations is five at one locus, six at the other two microsatellite loci and is three, on average, per population. Het erozygosities range from 0.18 to 0.74. The largest differences in alle lic frequencies occurred between the Mediterranean and the Atlantic po pulations: this result is congruent with previous allozymic data. The gene-centromere distances of the three microsatellite markers were det ermined 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 applicati on in genetic studies in salmonid species and fishes in general.