Making my usual TAE agarose gel for electrophoresis of some DNA constructs I am attempting to make, I was wondering about some of the 'lab wisdom' that I have received over the years. I think molecular biology is particularly full of superstitions passed from person to person. Probably because it is such usually a 'means to an end' instead of actual science. Specifically I was wondering about the practice on our research floor of cooling the molten agarose to below 70C before addition of Ethidium Bromide (EtBr). The wisdom is that if EtBr is added before the agarose cools you are exposing yourself to vapours containing EtBr. Not good if you know about EtBr.
Quickly, EtBr is a chemical often used to visual DNA in agarose gels. It intercalates between DNA strands and in such an environment is a fluorescent orange/gold colour. Useful, yes. Also it is a mutagen, as determined by the Ames test. According to the Ames test EtBr is somewhere between mothballs and a cigarette in terms of mutagenicity. I guess this is not surprising because of its intimate interaction with DNA.
Lab wisdom is often suspect, as the previous link discusses. Check out some forum discussions on the very topic of EtBr in agarose gels. Scientists apparently like to talk about anecdotal evidence.
My favourite example of bad lab wisdom is about ethanol precipitations of DNA. Most people when performing this common procedure keep the solution of DNA, salt and ethanol on ice or at -20C for a certain time before centrifugation to pellet the precipitated DNA. You can be the biggest annoying know-it-all if, next time you see someone doing this, slap down this reference. This says that this cooling is completely unnecessary and can actually decrease yields. I keep a couple printed out on my bench for just such occasions.
A quick look at the MSDS for EtBr reveals that its vapour pressure is undetermined as is its mutagenic and carcinogenic potential. Sounds like this particular lab wisdom is unfounded but in this case perhaps it is wise.
Any other examples of bad lab wisdom that you happen to know about? Pass it on to the bayblab so that we can correct everyone in a very annoying, know-it-all manner.
[the festive agarose gel was ganked from tim holzer.]