Bioinformatics Molecular Biology

DNA Microarrays

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Scientists know that a mutation or any change in a particular gene’s DNA may present to a certain disease. However, it can be very difficult for them to make a test to detect these mutations, because most large genes have many regions where mutations can occur. But there is not one specific mutation responsible for all of these cases. For this purpose, the DNA microarray technique used to determine whether the DNA from a particular individual has a mutation in genes or not.

The chip has a small glass plate encased in plastic. Some companies manufacture microarrays using methods similar to those used to make computer microchips. On the surface, each chip has thousands of short, synthetic, single-stranded DNA sequences, which together add up to the normal gene in question, and to variants (mutations) of that gene that have been found in the human population.

Uses 

  • Used to study the range to which certain genes are turned on or off in cells and tissues
  • In clinical diagnostic tests for some diseases
  • Used to determine which drugs might be best prescribed for particular individuals
  • Used in DNA sequencing 
  • To determine whether an individual has a mutation for a particular disease
  • Helps in the identification of new genes, know about their functioning and expression levels under different conditions
  • Microarray technology helps researchers learn more about different diseases such as heart diseases, mental illness, infectious disease and especially the study of cancer
  • Extensive use in Pharmacogenomics
  • It provides a robust platform for the research of the impact of toxins on the cells and their passing on to the progeny

The researcher denatures the DNA in the samples, a process that separates the two complementary strands of DNA into single-stranded molecules. The next step is to cut the long strands of DNA into smaller, more manageable fragments and then to label each fragment by attaching a fluorescent dye. The individual’s DNA is labeled with green dye and the control or normal DNA is labeled with red dye. Both sets of labeled DNA are then inserted into the chip and allowed to hybridize or bind to the synthetic DNA on the chip.

If the individual does not have a mutation for the gene, both the red and green samples will bind to the sequences on the chip that shows the sequence without the mutation.

If the individual does contain a mutation, the individual’s DNA will not bind properly to the DNA sequences on the chip that represent the “normal” sequence but instead will bind to the sequence on the chip that represents the mutated DNA.

The process in which the cDNA molecules bind to the DNA probes on the slide is called hybridization. Following hybridization, the microarray is scanned to measure the expression of each gene printed on the slide. If the expression of a particular gene is higher in the experimental sample than in the reference sample, then the corresponding spot on the microarray appears red. In contrast, if the expression in the experimental sample is lower than in the reference sample, then the spot appears green. Finally, if there is equal expression in the two samples, then the spot appears yellow. The data gathered through microarrays can be used to create gene expression profiles, which show simultaneous changes in the expression of many genes in response to a particular condition or treatment.

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