Fundamental techniques used in molecular biology can be applied toward questions of relevance to epilepsy. Many of the most common techniques used for working with nucleic acids, including DNA extraction, electrophoresis, cloning in plasmid vectors, making probes, and the polymerase chain reaction are now commonly used in basic epilepsy research. Some specific approaches that can be used to address particular questions are methods for identifying a human gene (Southern analysis and screening a library), determining whether a gene is expressed in a given brain region (Northern analysis and in situ hybridization), and expressing a gene in tissue culture or a whole organism (cell transfection and transgenic animals).