HPV genotyping of cervical cancer tissue specimens. (A) A first run of the HPV general standard pattern followed by the PCR product of four unknown samples. (B) The second run mixes the unknown samples with HPVs from group IV. Because each sample in the mixture produces a sharp peak, it is easy to deduce that the sequence of sample 408 is identical to that of HPV type 18, that the sequence of sample 162 matches that of HPV type 52, and that the sequence of sample 246 matches that of HPV type 45. (C) A second run that mixes unknown samples with HPV type 16 by using group I conditions. The peaks produced by samples 271, 391, and 419 contain a shoulder; sequencing of the PCR product revealed an HPV type 16 variant.