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specific conditions only detect the two alleles at a single locus and generate what have

been termed DNA profiles because, unlike multilocus probes, the two-band pattern

result is in itself insufficient to uniquely identify an individual.

Techniques based on the PCR have been coupled to the detection of minisatellite

loci. The inherent larger size of such DNA regions was not best suited to PCR

amplification; however, new PCR developments are beginning to allow this to take

place. The discovery of polymorphisms within the repeating sequences of minisatellites

has led to the development of a PCR-based method that distinguishes an individual on

the basis of the random distribution of repeat types along the length of a person’s two

alleles for one such minisatellite. Known asminisatellite variant repeat(MVR) analysis

ordigital DNA typing, this technique can lead to a simple numerical coding of the

repeat variation detected. Potentially this combines the advantages of PCR sensitivity

and rapidity with the discriminating power of minisatellite alleles. Thus for the future

there are a number of interesting identification systems under development and

evaluation. Techniques for genetic detection of polymorphisms have been used in

many cases of paternity testing and immigration control, and are becoming central

factors in many criminal investigations. They are also valuable tools in plant biotech-

nology for cereal typing and in the field of pedigree analysis and animal breeding.

6.8.8 Microarrays and DNA microchips

One firmly established area under rapid development in molecular biology is the use of

microarrays orDNA microchips. These provide a radically different approach to current

laboratory molecular biology research strategies in that large-scale analysis and quanti-

fication of genes and gene expression is possible simultaneously. A microarray consists

of an ordered arrangement of potentially hundreds of thousands of DNA sequences such

Table 6.5Main methods of detecting mutations in DNA samples

Technique Basis of method Main characteristics of detection

Southern blotting Gel based Labelled probe hybridisation to DNA

Dot/slot blotting Sample application Labelled probe hybridisation to DNA

Allele-specific oligo-PCR
(ASO–PCR)

PCR based Oligonucleotide matching to DNA sample

Denaturing gradient gel
electrophoresis (DGGE)

Gel/PCR based Melting temperature of DNA strands

Single-stranded conformation
polymorphism (SSCP)

Gel/PCR based Conformation difference of DNA strands

Ligase chain reaction (LCR) Gel/automated Oligonucleotide matching to DNA sample

DNA sequencing Gel based Nucleotide sequence analysis of DNA

DNA microchips Glass chip based Sample DNA hybridisation to oligo arrays

252 Recombinant DNA and genetic analysis