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▲ EXPERIMENTAL FIGURE 10-7 Probes for minisatellite DNA can reveal unique restriction fragments (DNA fingerprints) that distinguish individuals. DNA samples from three Individuals (1, 2, and 3) were subjected to Southern blot analysis using the restriction enzyme Hinfl and three different labeled minisatellites as probes (lanes a, b, and c). DNA from each individual produced a unique band pattern with each probe. Conditions of electrophoresis can be adjusted so that for each person at least 50 bands can be resolved with this restriction enzyme. The nonidentity of these three samples is easily distinguished. [From A. J. Jeffreys et al., 1985, Nature 316:76; courtesy of A. J. Jeffreys.]

thought to result from unequal crossing over within regions of simple-sequence DNA during meiosis (Figure 10-6). As a consequence of this unequal crossing over, the lengths of some tandem arrays are unique in each individual.

In humans and other mammals, some of the satellite DNA exists in relatively short 1- to 5-kb regions made up of 20-50 repeat units, each containing 15 to about 100 base pairs. These regions are called minisatellites to distinguish them from the more common regions of tandemly repeated satellite DNA, which are »20-100 kb in length. They differ from microsatellites mentioned earlier, which have very short repeat units. Even slight differences in the total lengths of various minisatellites from different individuals can be detected by Southern blotting of cellular DNA treated with a restriction enzyme that cuts outside the repeat sequence (Figure 10-7). The polymerase chain reaction (PCR), using

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