A linkage map of the Atlantic salmon (Salmo salar) based on EST-derived SNP markers

Thomas Moen¹^,2 , Ben Hayes¹^,2 , Matthew Baranski¹^,2 , Paul R Berg¹^,3 , Sissel Kjøglum⁴ , Ben F Koop⁵ , Willie S Davidson⁶ , Stig W Omholt¹^,3 and Sigbjørn Lien¹^,3

¹CIGENE – Centre of Integrative Genetics, Ås, Norway

²AKVAFORSK – Institute of Aquaculture Research, Ås, Norway

³Institute of Animal and Aquacultural Sciences, Norwegian University of Life Science, Ås, Norway

⁴Aqua Gen AS, Trondheim, Norway

⁵Centre for Biomedical Research, Department of Biology, University of Victoria, Victoria, British Columbia, Canada

⁶Department of Molecular Biology and Biochemistry, Simon Fraser University, Burnaby, British Columbia, Canada

author email corresponding author email

BMC Genomics 2008, 9:223doi:10.1186/1471-2164-9-223


Published:	15 May 2008

Abstract

Background

The Atlantic salmon is a species of commercial and ecological significance. Like other salmonids, the species displays residual tetrasomy and a large difference in recombination rate between sexes. Linkage maps with full genome coverage, containing both type I and type II markers, are needed for progress in genomics. Furthermore, it is important to estimate levels of linkage disequilibrium (LD) in the species. In this study, we developed several hundred single nucleotide polymorphism (SNP) markers for the Atlantic salmon, and constructed male and female linkage maps containing SNP and microsatellite markers. We also investigated further the distribution of male and female recombination events across the genome, and estimated levels of LD between pairs of markers.

Results

The male map had 29 linkage groups and was 390 cM long. The female map had 30 linkage groups as was 1983 cM long. In total, the maps contained 138 microsatellite markers and 304 SNPs located within genes, most of which were successfully annotated. The ratio of male to female recombination events was either close to zero or very large, indicating that there is little overlap between regions in which male and female crossovers occur. The female map is likely to have close to full genome coverage, while the majority of male linkage groups probably lack markers in telomeric regions where male recombination events occur. Levels of r²increased with decreasing inter-marker distance in a bimodal fashion; increasing slowly from ~60 cM, and more rapidly more from ~12 cM. Long-ranging LD may be consequence of recent admixture in the population, the population being a 'synthetic' breeding population with contributions from several distinct rivers. Levels of r²dropped to half its maximum value (above baseline) within 15 cM, and were higher than 0.2 above baseline for unlinked markers ('useful LD') at inter-marker distances less than 5 cM.

Conclusion

The linkage map presented here is an important resource for genetic, comparative, and physical mapping of the Atlantic salmon. The female map is likely to have a map coverage that is not far from complete, whereas the male map length is likely to be significantly shorter than the true map, due to suboptimal marker coverage in the apparently small physical regions where male crossovers occur. 'Useful LD' was found at inter-marker distances less than 5 cM.