DNA is a large polymer consisting of two DNA strands that form a double helix. Each strand is made up of bases. In DNA, there are four different bases:Adenine, Thymine, Cytosine & GuaninePairs of bases form chemical cross-links between the two strands of DNA to form the final double helix. The base pairs always form a particular way:- Adenine always pairs with Thymine (A --- T)- Cytosine always pairs with Guanine (C --- G)This process is called complementary base pairing.