The DNA (deoxyribonucleic acid) is a hereditary molecules, which is passed from one generation to another. A DNA molecule is made up nucleotides, each nucleotide is made of a sugar, a phosphate group and a nitrogenous base.
There are 4 types of nitrogenous bases present in the DNA, adenine, guanine, cytosine and thymine.
All the organism are made up of DNA only, which suggest that all the organism are derived from a single ancestor, as on the molecular level all the organism have a single type of molecules which determines all the traits in the organism.