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techniques used to detect known or unknown mutations are indicated in Table 6.5.

An extension of this principle is used in a number of detection methods employing

denaturing high-performance liquid chromatography (dHPLC). Commonly known as

wave technologythe detection of denatured single strands containing mismatches is

rapid allowing a high-throughput analysis of samples to be achieved.

6.8.7 Detecting DNA polymorphisms

Polymorphisms are particularly interesting elements of the human genome and as such

may be used as the basis for differentiating between individuals. All humans carry

repeats of sequences known asminisatellite DNAof which the number of repeats

varies between unrelated individuals. Hybridisation of probes which anneal to these

sequences using Southern blotting provides the means to type and identify those

individuals (Section 5.3).

DNA fingerprintingis the collective term for two distinct genetic testing systems

that use either ‘multilocus’ probes or ‘single-locus’ probes. Initially described DNA

fingerprinting probes were multilocus probes and so termed because they detect

hypervariable minisatellitesthroughout the genome, i.e. at multiple locations within

the genome. In contrast, several single-locus probes were discovered which under

Sample DNA with mutation

PCR with GC clamp

Separate by electrophoresis
in gradient of denaturant

Duplex

melting

Duplex

melting

Mutated

DNA

Normal

DNA

Fig. 6.46Detection of mutations using denaturing gradient gel electrophoresis (DGGE).

251 6.8 Analysing genes and gene expression