1. A gaming system comprising: a display for symbols to be displayed in a set of display positions to a player; a symbol selector for selecting in each game round a plurality of symbols for display to the player in a set of display positions; a cloned symbol controller arranged to modify the displayed symbols by copying each symbol in an original subset of the display positions to at least one clone subset of the display positions which is identical to or laterally displaced from the original subset, in response to determining that a subset of the symbols should be cloned; and an outcome generator arranged to determine an outcome based on the modified symbols; wherein the cloned symbol controller is arranged to retain the cloned symbols during one or more following cloned symbol game rounds; wherein the game controller is arranged to restrict the symbol selection in the following cloned symbol game rounds so that the reel positions for reels containing the clone subset and the original subset are fixed relative to each other; and wherein the original subset is all the visible positions of an original reel and the cloned subsets are all the visible positions of clone reels, and non-visible symbols on the original reel are also copied to corresponding non-visible positions on the clone reels, so that the original and clone reels show the same symbols in each visible reel position in the following cloned symbol game rounds.