A typical microarray experiment involves the hybridization of an mRNA molecule to the DNA template from which it is originated. Many DNA samples are used to construct an array. The amount of mRNA bound to each site on the array indicates the expression level of the various genes. This number may run in thousands. All the data is collected and a profile is generated for gene expression in the cell.

Watch this video for a better understanding of microarray expermient

A DNA “chip” or microarray is prepared on a small solid base such as a piece of glass  divided into a grid of tiny squares. To each square is attached a different and specific piece of DNA, typically a short DNA sequence that can act as a probe for a particular gene. DNA corresponding to thousands of different genes can be accommodated on a single array no bigger than a microscope slide.

A single stranded DNA sample of interest is cut up and then washed over the chip. Any sequence in the sample that matches a sequence on the chip will hybridise to it and, if the sample is suitably labeled (usually with a fluorescent tag) the pattern of matches can be visualised and analysed by computer, giving a read-out of the presence or expression level of hundreds of different sequences simultaneously.

To explain the microarray process in a few steps a figure has been provided below.

Steps followed in a Microarray Experiment

Steps followed in a Microarray Experiment

Why are Microarray’s important?

Microarrays are useful when one wants to survey a large number of genes quickly or when the sample to be studied is small. Microarrays may be used to assay gene expression within a single sample or to compare gene expression in two different cell types or tissue samples, such as in healthy and diseased tissue. Because a microarray can be used to examine the expression of hundreds or thousands of genes at once, it promises to revolutionize the way scientists examine gene expression. This technology is still considered to be in its infancy; therefore, many initial studies using microarrays have represented simple surveys of gene expression profiles in a variety of cell types. Nevertheless, these studies represent an important and necessary first step in our understanding and cataloging of the human genome.

With new advances, researchers will be able to infer probable functions of new genes based on similarities in expression patterns with those of known genes. Ultimately, these studies promise to expand the size of existing gene families, reveal new patterns of coordinated gene expression across gene families, and uncover entirely new categories of genes. Furthermore, because the product of any one gene usually interacts with those of many others, our understanding of how these genes coordinate will become clearer through such analyses, and precise knowledge of these inter-relationships will emerge. The use of microarrays may also speed the identification of genes involved in the development of various diseases by enabling scientists to examine a much larger number of genes. This technology will also aid the examination of the integration of gene expression and function at the cellular level, revealing how multiple gene products work together to produce physical and chemical responses to both static and changing cellular needs.

Types of Microarray:

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