Gaming device with a changing arrangement of symbol display positions

A gaming system comprising:

• at least one processor;
• and
• a memory storing (a) a current symbol position state defining, for each of a plurality of columns of symbol positions, a number of symbol positions for which symbols are to be selected;
• (b) a pay table;
• and (c) instructions which when executed by the at least one processor cause the at least one processor to:
• control a display to display the plurality of columns of symbol positions corresponding to the current symbol position state;
• select symbols for the displayed symbol positions by selecting stopping positions of a plurality of base reel strips based on one or more first returned values of a random number generator, each base reel strip of the plurality of base reel strips associated with a respective one of the columns;
• determine, by selecting stopping positions of a plurality of overlay reel strips based on one or more second returned values of the random number generator, whether to map at least one designated symbol to a first displayed symbol position, wherein the designated symbol indicates a change in the symbol position state;
• replace, in response to a determination to map a designated symbol to a first displayed symbol position, the selected symbol from the plurality of base reel strips corresponding to the first displayed symbol position with the designated symbol;
• evaluate the selected symbols for winning combinations based on the pay table;
• and
• modify, in response to the selected symbols of a column including a designated symbol, the symbol position state for the respective column to include at least one additional symbol position for a next symbol selection.