When living cells were exposed to either mobile phone radiation or gamma rays from a radioactive isotope (one tenth of the lethal dose for humans) we see considerable DNA damage. In these experiments, which were part of the Reflex Project, sponsored by the European Commission, small fragments of broken DNA stream out of the cells like the tail of a comet. The size of the tail is a measure of DNA damage. The sham exposure was not irradiated and the DNA is intact.
We can see the DNA by using a fluorescent dye which binds to DNA and lights up under ultra violet light. These pictures were obtained using micro-gel electrophoresis which involves irradiating living cells, putting them in a jelly on a microscope slide, treating them with chemicals to remove their membranes and then applying a voltage across the slide to draw out the electrically-charged DNA fragments.