Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/1/2004
Publication Date: 4/1/2004
Citation: Woram, R.A., Mcgowan, C., Stout, J.A., Gharbi, K., Ferguson, M.M., Hoyheim, B., Davidson, W.S., Rexroad III, C.E., Danzmann, R.G. 2004. A genetic linkage map for arctic char (salvelinus alpinus): evidence for higher recombination rates and segretation distortion in hybrid versus pure strain mapping parents. Genome. 47:304-315.
Interpretive Summary: Linkage map construction facilitates a number of important biological investigations including comparative mapping among species, searching for genes controlling physiological traits, and the study of evolutionary processes. We constructed a genetic linkage map for Arctic charr (Salvelinus alpinus) using two backcrosses between genetically divergent strains. Analysis of 326 DNA markers and the SEX phenotype on these crosses resulted in forty-six linkage groups (expected = 39) which were used to investigate differences in recombination rates between individuals. Female recombination rates were often significantly higher than those of males. These findings do not support the proposition that hybridization may reduce recombination rates within the hybrid individual. Outcrossing in salmonids may in fact elevate general recombination levels in the hybridized genomes of the new strain, at least for the first few generations following hybridization. The generality of this statement awaits further empirical testing in other species and across more strains.
Technical Abstract: We updated the genetic map of rainbow trout (Oncorhynchus mykiss) for two outcrossed mapping panels (SAKAMOTO et al. 2000), and used this map to assess the putative chromosome structure, and recombination rate differences among the various linkage groups within the species. We then used the rainbow trout sex specific maps to make comparisons with two other ancestrally polyploid species of salmonid fishes, Arctic charr (Salvelinus alpinus), and Atlantic salmon (Salmo salar), to: identify homeologous chromosome affinities within each species and ascertain homologous chromosome relationships among the species. Salmonid fishes appear to have the largest sex-specific differences in recombination rate for any vertebrate species studied to date. Our current estimate of female : male recombination rates in rainbow trout is 4.31 : 1. Chromosome structure and/or size was also observed to have a profound influence on recombination rate differences between the sexes in rainbow trout. Linkage groups derived from presumptive acrocentric type chromosomes were observed to have much lower sex-specific differences in recombination rate than metacentric type linkage groups. Arctic charr is karyotypically the least derived species (i.e. possessing a high number of acrocentric chromosomes) and Atlantic salmon is the most derived (i.e. possessing a number of whole-arm fusions). Atlantic salmon have the largest female : male recombination ratio difference (i.e. 16.33 : 1) in comparison to rainbow trout, and Arctic charr (1.69 : 1). Comparisons of recombination rates between homologous segments of linkage groups among species indicated that when significant experiment-wise differences were detected (7 / 24 tests), recombination rates were higher in the species with a less derived chromosome structure. However, one parental comparison between Atlantic salmon and rainbow trout did not support this finding. Greater similarity in linkage group syntenies were observed between Atlantic salmon and rainbow trout suggesting their closer phylogenetic affinities, and most interspecific linkage group comparisons support a model that suggests whole chromosome arm translocations have occurred in the evolution of this group. However, some possible exceptions to this rule were detected and these findings are discussed in relation to their influence on segregation distortion patterns detected in rainbow trout. We also report an apparent rare instance of a pseudolinkage affinity in one of our female mapping parents. This pseudolinkage involved the duplicated (homeologous) linkage group pair 12/16.