show Abstracthide AbstractThreespine stickleback Gasterosteus aculeatus is an excellent model to study adaptation genomics. Marine and freshwater morphs of threespine sticklebacks differ from each other in a number of morphological, physiological and bihavioral traits, but retain the ability to mate and produce fertile offspring. We sequenced individuals from two marine and two freshwater populations in order to find substitutions responsible for adaptation to fresh water. We also sequenced additional populations: from two lakes and two quarries, to measure densities of freshwater alleles in marker SNPs in these populations.