DNA microarrays are special slides that allow all the genes in a cell to be studied in one go. They can show which genes in a specific cell are switched on and which are switched off and they allow one type of cell to be compared with another. They work by taking mRNA from the two different cells, then mark it with a fluorescent labelling mix (to colour it and make it into cDNA) and then apply it in a solution to a specially prepared slide. This slide has a polymerase chain reaction (PCR) applied to it by a computer to make one side of the DNA strain for each individual gene. So when the marked genes are applied they all attach to the corresponding strain.
When two different sets of genes are applied they both have different colours such as red and green. If only the red set of genes have a certain gene switched on then the spot for that gene will become red. If only the green set of genes have the gene switched on then the spot will turn green. If both sets of genes have the gene switched on then that spot will turn yellow. This means that the people studying the microarray can compare the two genomes and see, by means of the colour code, which genes are activated in specific cells.
Using microarrays has a number of advantages, the main one being that they allow the behaviour of many genes to be studied at once. They can be used to study cancerous cells to see which genes have been switched on and off in the cells. They can also be used to diagnose genetic disorders. Using microarrays is also relatively cheap and easy whilst also being much safer than other methods (as no radioactive or toxic elements are involved).