Genetic analysis of a development rate QTL in backcrosses of clonal rainbow trout, Oncorhynchus mykiss

Backcrosses of clonal rainbow trout, Oncorhynchus mykiss, were used in an effort for fine-mapping of a quantitative trait locus (QTL) for rapid embryonic development rate (tth-1). A previously identified QTL was backcrossed for two successive generations from the Clearwater (fast developing) line into the Oregon State University (OSU) (slow developing) background. Microsatellites tightly linked to the QTL and each other were used to genotype individuals in both backcrosses. An association was found between the microsatellites and gamete production in the first backcross and precocious gamete production in the second backcross generation. These results suggest that a region near the QTL-linked microsatellites may influence early sexual maturity, as well as development rate. Two gynogenetic families were produced using individuals from the first backcross (BC1). These crosses were screened with the tth-1 linked microsatellites and time to hatch was quantified. The Clearwater genotype was associated with early time to hatch, while the OSU genotype was associated with late hatching. Genotypic variation at these microsatellite loci explained 28% and 26% of the variation in time to hatch. Heterozygote frequencies for the microsatellites in the two gynogenetic families were 0.0088 and 0.01, suggesting that the QTL is near the centromere. Fine-mapping was limited due to the low level of recombination observed on this linkage group in the gynogenetic families.