When two or more DNA sequences are aligned, the overlapping portions can be combined to create a single consensus sequence. In positions where all overlapping sequences have the same base (a single column of the multiple alignment), that base becomes the consensus. Various rules may be used to generate the consensus for positions where there are disagreements among overlapping sequences. A simple majority rule uses the most common letter in the column as the consensus. Any position where there is disagreement among aligned bases can be written as the letter N to designate “unknown.” There is also a set of IUPAC ambiguity codes (YRWSKMDVHB) that can be used to specify specific sets of different DNA bases that may occupy a single position in the consensus.