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]. In the DNA microarrays, there are closely packed gene-specific sequences are exist and they are bound to the surface of a glass microscope slide [3]. The DNA microarray consists of a flat surface to which oligonucleotides are bound [2]. These oligonucleotides are complementary to specific cDNA sequences [2]. Additionally, the oligonucleotides generally around 20 nucleotides lenght and they are synthesised from the previously attached gene-specific sequences to the glass microscope slide Cite error: Invalid <ref> tag; name cannot be a simple integer. Use a descriptive title. 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].
References
- ↑ http://learn.genetics.utah.edu/content/labs/microarray/
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 Daniel L. Hartl, Elizabeth W. Jones (2009) Genetics Analysis of Genes and Genomes 7th Edition USA, Jones and Bartlett Publishers.
- ↑ Lodish H., Berk A., Kaiser C A., Krieger M., Bretscher A., Ploegh H., Amon A., Scott M P. (2013) Molecular Cell Biology, 7th Edition, New York: W.H. Freeman and Company