Question

What is the science behind microarray methods and how it does work?

Answer 1

An array is an orderly arrangement of samples where matching of known and unknown DNA samples is done based on base pairing rules.It genotypes multiple regions of a genome or to generate lists of expressed genes from a cell.

PRINCIPLE
complementary sequences will bind to each other. The unknown DNA molecules are cut into fragments by restriction endonucleases, them  fluorescent markers are attached to these DNA fragments then allowed to react with probes of the DNA chip.
Working
mRNA are collected from diseased and healthy patients and then converted to cDNA
sample is labeled with a fluorescent probe of a different color, diseased with red dye and healthy with green.
The process in which the cDNA molecules bind to the DNA probes on the slide is called hybridization
The fluorescently labeled complimentary DNA is loaded onto the microarray, where thousands of single-stranded DNA samples (corresponding to a single gene) are arranged as spots in a grid formation.
If the expression of a particular gene is higher in the diseased sample than in the healthy sample, then the corresponding spot on the microarray appears red.
if the expression in the disease sample is lower than in the healthy sample, then the spot appears green.
So, we say When the fluorescently labeled cDNA binds to the complimentary base pairs within the sample spot, then the gene is shown to be active.
So, It is used to  create gene expression profiles, which show simultaneous changes in the expression of many genes in response to a particular condition or treatment.