• Genes are present inside the chromosome, which are the basic physical and functional units of hereditary.
     

• Genes are made up of specific sequences of bases and these gene bases, code for specific protein production as needed by the human body for normal metabolism.
     

• Proteins are required for normal cellular function, proper functioning of proteins is required for production and maintaining of cellular structures.
    

• When alterations in gene takes place the proteins which are coded by these gene are not able to function and causes genetic disorders.
    

• Gene therapy is done to repair the defective genes responsible for disease. Gene therapy is done by: 
  

            1. Inserting the normal gene into the genome to replace the non 
                functional gene.
 
            2. By recombination: The abnormal gene is replaced by normal gene.
 
            3. By selective reverse mutation: The abnormal gene is repaired to 
               become normal and perform  its normal function.