A method for determining the number of nucleic acid molecules (NAMs) in a group of NAMs, comprising i) obtaining an amplified and mutagenized group of NAMs that was produced by a. subjecting the group of NAMs to a chemical mutagenesis which mutates only select nucleic acid bases in the group of NAMs at a rate of 10% to 90% thus forming a group of mutagenized NAMs (mNAMs), and b. amplifying the group of mNAMs; ii) obtaining sequences of the mNAMs in the group of amplified mNAMs; and iii) counting the number of different sequences obtained in step (ii) to determine the number of unique mNAMs in the group of mNAMS, thereby determining the number of NAMs in the group of NAMs.