DNA microarrays
DNA microarrays[1] are used in functional genomics to determine the differences in gene expression levels between a sample and control cell [2]. The sample cell can be: from a different tissue, at a different stage of development, at a different stage of the cell cycle, or be under different conditions (for example, exposure to a toxin) [2]. The DNA microarray consists of a flat surface to which oligonucleotides are bound [2]. These oligonucleotides are complementary to specific cDNA sequences [2]. The mRNA molecules within the sample and the control are converted into labelled cDNA molecules with the use of reverse transcriptase and fluorescently-labelled nucleotides[2].
For example, the cDNA of the sample can have a red fluorescence label whereas the cDNA of the control can have a green fluorescence label [2]. The DNA microarray is exposed to the cDNA mixture and unbound cDNA is washed away [2]. The resultant DNA microarray consists of spots of colour that is imaged using a confocal fluorescence scanner [2]. The colour of the spot is indicative of the differences in gene expression between the sample and control [2]. Following the colour scheme above, a red spot indicates that the sample is overexpressing that particular gene compared to the control; a green spot indicates that the sample is underexpressing that particular gene compared to the control; and a yellow spot indicates that there is equal gene expression in the sample and control [2]. However, the range of colours is not as discrete as suggested here, it is more of a spectrum covering intermediate differences in gene expression[2]. DNA microarrays are not so useful in determining gene function but can ascertain which genes may have the same regulatory mechanisms[2].
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