Identification of two QTL influencing upper temperature tolerance in three rainbow trout (Oncorhynchus mykiss) half-sib families

We searched for linkage among 24 polymorphic loci (allozymes, RAPD, microsatellites) in three half-sib backcross families of rainbow trout (Oncorhynchus mykiss) produced by crossing strains divergent for the quantitative trait of upper temperature tolerance. Seven significant and two suggestive pairwise linkage associations between molecular marker loci were observed involving 14 loci clustered into four linkage groups. The association between a pair of allozyme loci (sIDHP-3* and mMEP-2 *) has been reported previously. Recombination rates varied greatly between the sexes and families. Two quantitative trait loci (QTL) were mapped by detecting a significant association between variance in upper temperature tolerance and alleles at the microsatellite loci Omy325UoG and Ssa14DU. The two QTL appear to reside in different linkage groups and account for ≈13 per cent and 9 per cent of the overall additive genetic variance in upper temperature tolerance. No significant interaction was detected between Omy325UoG and Ssa14DU suggesting that the effects of the QTL are additive.