DNA is the abbreviation for deoxyribonucleic acid. It is found in every cell within the human body. It is composed of nucleotides, which are composed of four bases: adenine, thymine, cytosine, and guanine. Each of the bases are abbreviated by the first letter in their names, A, T, C, and G. There are over three billion nucleotides in the human genome as a whole, which accounts for 99.9% identicality from one human being to the next. It is the .1% of variation which allows the analysis of DNA to be used as an identification tool in identifying people. The part of the DNA where the variation is the greatest is found in a part called the intron, which is a section of the genes that are not part of the protein the gene encodes. This part is usually spliced out during the processing of messenger RNA, which represents an intermediate molecule while the DNA is encoding for the protein. This method of fingerprinting is very accurate. Cells used for DNA extraction are typically hair or blood. The only exception to this type of fingerprinting is in the case of identical twins, who possess identical genetic sequences.