Positions of functionally important spacers compared to positions of all spacers. Targeting (A) and shared (B) spacers are presented. Spacers in each cassette were enumerated. For each cassette, serial numbers of all targeting (resp., shared) spacers in the cassette were summarized, and then the obtained statistics was summarized for the whole set of cassettes (the red dashed line). The plot shows the distribution of sums of serial numbers of targeting (resp., shared) spacers for the shuffled sets of cassettes (100,000 permutations) (see Methods).