FIG. 7.

Multiple losses of PCR-amplified DNA regions due to independent nucleotide substitutions in the two priming regions. (a) PCR amplification of a DNA sequence showing incorporation of the primer oligonucleotides at each end of the sequence. (b) Failure of PCR amplification due to a G-to-A transition that defeats priming at the left-hand priming region. (c) Failure to amplify DNA due to a second transition that defeats priming at the right-hand priming region.