COMPOSITE INTERVAL MAPPING REVEALS A QTL OF MAJOR EFFECT ON EMBRYONIC DEVELOPMENT RATE IN RAINBOW TROUT (Oncorhynchus mykiss).

School of Biological Sciences Washington State University Pullman, WA 99164-4236

Little is known about the genetics controlling the rate of embryonic development in salmonids, despite the fact that this trait plays an important role in the life history of wild and cultured stocks. In order to investigate the genetics of embryonic development rate, a QTL analysis was performed on two families of androgenetically derived doubled haploid rainbow trout produced from a hybrid of two clonal lines with divergent embryonic development rate phenotypes. A total of 171 doubled haploid individuals were genotyped at 222 marker loci (219 AFLP markers, 2 microsatellites, and p53). A genetic linkage analysis resulted in a map consisting of 26 linkage groups with 17 of the markers remaining unlinked at a minimum LOD of 4.0 and maximum distance of 30 cM. Several of these linkage groups were matched to linkage groups from the published rainbow trout linkage map. Composite Interval Mapping (CIM) revealed a single QTL which had a significant effect on both embryonic development rate (LOD 8.2) and length at yolk absorption (LOD 5.3). This QTL explained 32.9% and 18.5% of the variance in development rate in doubled haploid families one and two, respectively. The QTL also explained 17.5% of the variance in embryonic length. The most likely position of the QTL was at a previously unmapped AFLP locus on linkage group IX of the published linkage map. These results have significant implications for genetic improvement of cultured rainbow trout through Marker Assisted Selection and for the study of naturally occurring genetic variation.