DNA PROBES

=DNA Probes= [image:http://i.imgur.com/fnP78XQ.png?1] DNA probes are simply oligonucleotides (short sequences of DNA) approx 100-1000bp long, that are used to detect the presence of complimentary sequences. Usually the probe is labelled with a fluorescent dye or radioactive isomer. When the probe is mixed with a sample of DNA it will hybridise (stick to) any regions / fragments with a complementary sequence. Using a probe allows the target sequence to be seen under UV light or on an X-ray film. DNA probes are often used to highlight specific DNA fragments that have been separated by Gel Electrophoresis. One application of this technique is ‘chromosome painting’. Here probes carrying different coloured fluorophores (fluorescent molecules) are made that correspond to sequences on each of the human chromosomes. Effectively each chromosome can be ‘painted’ a different colour, making it much easier to construct a karyotype. Probes can also be used to identify genetic defects.