EXPERIMENTAL FIGURE 6-24 Southern blotting can detect a specific DNA fragment in a complex mixture of restriction fragments. The diagram depicts three different restriction fragments in the gel, but the procedure can be applied to a mixture of millions of DNA fragments. Only fragments that hybridize to a labeled probe will give a signal on an autoradiogram. A similar technique, called Northern blotting, detects specific mRNAs within a mixture. See E. M. Southern, 1975, J. Mol. Biol. 98:508.