Named after its UK inventor, Ed Southern, a ‘southern blot’ is a laboratory method that identifies specific types of sequence variant in DNA. It revolutionised molecular genetics in the 1980s by making it possible to produce systematic maps of genetic variation in health and disease. The pace of progress in molecular genetics was such that Southern blots were rapidly superseded by faster polymerase chain reaction (PCR)-based technologies that use much less DNA. They have been rarely used over recent years in DNA work, although related approaches are used with work on RNA (so-called ‘northern blots’) and proteins (so-called ‘western blots’).