Ethidium bromide and mutagenesis on cloning When performing a DNA cloning, sometimes PCR amplicon is run in agarose and it is detected by ethidium bromide marking under UV light. After that, gel is sliced, DNA extracted from gel....... until eventually you have your transgenic organism. The thing is that when doing so, you use the very same DNA sample that was "contaminated" by ethidium bromide, so does this DNA you are using for transformation contain ethidium bromide? if so, how can it affect in numbers to mutation risk?

Purified DNA contains negligible amounts of ethidium bromide. PCR and gel clean-up kits remove it quite well. There is, though, a risk of mutation from the fact that you're visualizing the gel in UV light with ethidium bromide. The risk of mutation from UV is minimized by exposing the gel as little as possible, and by using "preparative" transilluminators that come with a low-light setting for cloning purposes. If you work well and quickly, the chance of mutagenesis isn't higher than the chance of a polymerase incorporating the wrong nucleotide.