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... tissue containing cells with a nucleus (e.g. blood, a hair root or semen containing a few sperm cells) is taken to the laboratory where DNA is extracted by shaking the sample in a mixture of water-saturated phenol and chloroform. Proteins precipitate out, leaving pure DNA dissolved in the water layer. Some facts: Required amount of tissue: - 0.5 cm³ of blood - 0.005 cm³ of semen - one hair root Digestion Certain restriction enzymes are added to the DNA to cut it. The enzymes recognise specific base sequences and so cut only at specific points, close but not within the required minisatellite region. This process produces a no. of DNA fragments of different lengths, some of which contain the minisatellite. Separation 1. The DNA fragments are separated according to their size by electrophoresis: - DNA fragments are placed in wells at one end of a block of agarose gel. - An electric current is then passed through the gel. - The pieces ...