a common test for checking for a match between dna molecules. Dna fragments are separated by agarose gel electrophoresis, transferred (blotted) onto membrane filters, and hybridised with complementary radiolabelled probes. The aim is to detect specific base sequenceswith the probes. Lest all of this sound esoteric, note that in the television series The X files a southern blot was done (in this case, to learn if some alien virus genome had been integrated into a persons genome). The southern blot is named after its inventor, the British biologist M.E. Southern. There is also a northern blot and a western blot.