DNA stands for Deoxyribonucleic acid. DNA is the blueprint of any organism i.e. it governs all body functions (physiology), structure (anatomy) and to some extent behavior and psychological aspects too. Right from your height, hair color to your tendency towards serious health conditions like diabetes and hypertension is controlled largely by your DNA. All humans share 99.9% of their DNA. Only 0.1% of our DNA is different and that is what makes us unique, and different from any other person in the world.
Structurally, the DNA molecule is a double helix, a structure that looks much like a ladder twisted into a spiral. The two DNA strands (of the double helix) are composed of simpler units called nucleotides. These nucleotides are composed of one of the 4 nucleobases – adenine (A), guanine (G), thymine (T) or cytosine (C), and a phosphate and sugar molecule. Each of these bases pair up with a preferred partner e.g. A always pairs with T while a G always pairs with a C. Therefore, the A on one strand of the double helix pairs up with the T on the other strand, a G on one strand pairs up with a C on the other. In this manner, nucleotide pairs are arranged in a specific pattern within the DNA, and this pattern is unique for every individual.