Formalin-induced infidelity in PCR-amplified DNA fragments.

A 643-nucleotide-long fragment of rDNA gene was amplified by PCR in the nematode worm Caenorhabditis elegans. When the experiments were performed by using samples fixed in formalin, artefacts were detected. While the size of the amplified fragment resulted unaffected, very striking differences were seen in the nucleotide sequences of the amplified fragments. Furthermore, in many cases, the PCR reaction failed completely. The results obtained might warn of potential problems, especially when the amount of DNA to be amplified is scarce.