ucleotide chains, which can be many millions of nucleotides long, then wrap around one another to form the double helix structure, with every A group H-bonding to the T group on the adjacent chain (see here for A-T molfile), and every G group H-bonding to its matching C group (see here for G-C molfile).DNA - the source of heredityThe double helix of DNA controls heredity on the molecular level. The hereditary information is stored as the sequence of bases along the polynucleotide chain - a message written in a language of only 4 letters, A, C, G and T. DNA both preserves this information, and uses it. It does this through 2 properties:DNA molecules can duplicate themselves, in a process called replication, in which the 2 halves of the helix separate and a new partner is fabricated to exactly match each half.DNA molecules control the synthesis of the proteins which characterise each type of organism. The structure of DNA directly controls the structure of proteins, and the structure of proteins directly determines the way in which they control living processes. It would appear that biology is increasingly becoming a matter of the shapes and sizes of molecules.DNA FingerprintingSince the DNA within any species, and to any individual within that species, is unique, it can be used as a means of identification. DNA can be extracted from organic remains (blood, saliva, etc) left at crime scenes to identify the criminal. It can also be used to determine parentage, the gender of animals and birds (where it is difficult to do so by just looking at them!), and to prove whether traditional medicines contain extracts from endangered species. This process is called DNA fingerprinting....
