Health Information

DNA chips or DNA microarrays are recent developments for DNA sequencing as result of advances made in automation and miniarization. A large number of DNA probes, each one with different sequence, are immobilized at defined positions on the solid surface, made up of either nylon or glass. The probes can be short DNA molecules such as cDNAs or synthetic Oligonucleotides.

For the preparation of high density arrays, Oligonucleotides are synthesized in situ on the surface of glass or silicon. This results in an Oligonucleotide chip rather than a DNA chip.

Technique of DNA sequencing

A DNA chip carrying an array of different Oligonucleotides can be used for DNA sequencing. For this purpose, a fluorescently labeled DNA test molecule, whose sequence is to be determined, is applied to the chip. Hybridization occurs between the complementary sequences of the test DNA molecule and Oligonucleotides of the chip. The positions of these hybridizing Oligonucleotides can be determined by confocal microscopy. Each hybridizing Oligonucleotide represents an 8-nucleotide sequence that is present in the DNA probe. The sequence of the test DNA molecule can be deduced from the overlaps between the sequences of the hybridizing Oligonucleotides.

Application of DNA chips

There have been many successes with this relatively new technology of dna chips. Some of them are listed.
• Identification of genes responsible for the development of nervous systems.
• Detection of genes responsible for inflammatory diseases.
• Construction of microarrays for every gene in the genome of E.coli, and almost all the genes of the yeast Saccharomyces cerevisiae.
• Expression of several genes in prokaryotes has been identified.
• Detection and screening of single nucleotide polymorphisms (SNPs).
• Rapid detection of microorganisms for environmental monitoring.

The future of DNA chips

The major limitation of DNA chips at present is the unavailability of complete genome arrays for higher eukaryotes, including humans. It is expected that within the next few years such DNA chips will be available. This will help the biotechnologist to capture the functional snapshots of the genome in action for higher organisms.