A microsatellite linkage map of rainbow trout (Oncorhynchus mykiss) characterized by large sex-specific differences in recombination rates

We constructed a genetic linkage map for a tetraploid derivative species, t he rainbow trout (Oncorhynchus mykiss), using 191 microsatellite, 3 RAPD, 7 ESMP, and '7 allozyme markers in three backcross families. The linkage map consists of 29 linkage groups with potential arm displacements in the fema le map due to male-specific pseudolinkage arrangements. Synteny of duplicat ed microsatellite markers was used to identify and confirm some previously reported pseudolinkage arrangements based upon allozyme markers. Fifteen ce ntromeric regions (20 chromosome arms) were identified with a half-tetrad a nalysis using gynogenetic diploids. Female map length is similar to 10 M, b ut this is a large underestimate as many genotyped segments remain unassign ed at a LOD threshold of 3.0. Extreme differences in female:male map distan ces were observed (ratio F:M, 3.25:1). Females had much lower recombination rates (0.14:1) in telomeric regions than males, while recombination rates were much higher in females within regions proximal to the centromere (F:M, 10:1). Quadrivalent formations that appear almost exclusively in males are postulated to account for the observed differences.