DNA MICROARRAY
                                Introduction
      •  As  we  know  that  for  molecular  characterisation  of  any 
         gene/genome, nucleotide sequences are required.
      Understanding the genome function by analysing the genes 
         and the ways the genes expressed by the genome have a key 
         importance.
      There is  a  branch  of  biology  called  transcriptomics,  which 
         deals with gene expression in a tissue.
      It helps in studying the expression of genes by a genome both 
         qualitatively-  by  identifying  which  genes  are  expressed  and 
         which  are  not  expressed  and  qualitatively-  by  measuring 
         varying levels of expression  for different genes.
  So, transcriptome  analysis  reveals  gene  expression  profiles 
   that for the same genome may vary from cell to cell or from 
   tissue type to tissue type.
  Identifying  genes  expressed  by  a  genome  is  essential  for 
   understanding how the genome functions. 
  Gene  expression  can  be  checked  by  Northern  blotting 
   technique.
  But to  check  multiple  gene  expression  simultaneously,  we 
   developed a technique called DNA Microarray.
                What is DNA microarray
     DNA microarray, also known as gene chip is a solid support (like a glass 
     slide) onto which single stranded DNA molecules are attached.
     Each spot of DNA on glass slide called probe which represents a single 
     gene.
     It  is  widely  used  because  it  enables  researchers  to  analyze  all  of  a 
     sample’s expressed genes simultaneously.
     Microarray    technology  evolved  from  Southern  blotting  whereby 
     fragmented  DNA  is  attached  to  a  substrate  and  then  probed  with  a 
     known gene.
                  Principle
     It involves hybridisation of nucleotide sequences.
     Probe is complementary to target gene.
     Hybridisation produces signal.
        Requirements for cDNA based Microarray  
    Glass slide
    Probe (Attached to glass slide)
    Fluorescent dye
    Scanner
    Reverse transcriptase enzyme