Collecting a DNA sampleDNA is stored in the nucleus of each cell. This means that DNA can be harvested from any sample containing eukaryotic cells. Usually, a blood sample is collected, and DNA is then extracted from the white blood cells (red blood cells do not contain a nucleus). If blood sampling is impossible or too risky (children, animals, forensics), smaller amounts of DNA can also be extracted from a mouth swab (containing epithelial cells) or a few hair follicles.

DNA extraction可以从任何细胞中提取DNA。首先,我们需要to disrupt the cell (also known as cell lysis). This can be achieved using chemical and physical methods, grinding, or sonicating the cell. Once the cell is disrupted, we need to remove the membrane lipids by adding surfactants or detergents, digest the protein using protease, and remove RNA using RNase. Following this, we can precipitate DNA (for example, using ethanol) and isolate DNA from all other materials present in a cell. There are several methods that one can choose to extract DNA; one of the most popular methods is the use of phenol and chloroform; however, newer methods that are easier and safer have been developed, for example, using column separation.