►THE SCIENTIFIC BASIS OF DNA TYPING
DNA typing is founded on a number of genetic and molecular principles. Basic to the understanding of the complexity of DNA typing is the concept of the cell. A cell is the building unit of an organism made up of its component parts, one of which is the nucleus that functions as its command center. As the command center of the cell, the nucleus houses the DNA or deoxyribonucleic acid that codes for genetic information responsible for all cellular processes. Several DNA molecules comprise genes which in turn are located in minute bodies called chromosomes. In humans, there are 23 pairs of chromosomes within a cell thus making up a total of 46 chromosomes. Some chromosomal regions contain repeating units of the same type of DNA molecule which may or may not code for a specific protein. The number of repeating units in individuals may vary hence chromosomal regions with short tandem repeating DNA units (known as Short Tandem Repeat or STR markers) have been used as markers for human identification in forensic casework.
DNA can also be found in another part of the cell called the mitochondrion. Unlike nuclear DNA with two copies per cell, multiple copies of mitochondrial DNA (up to 100,000 copies) are present per human cell. Because of this, mitochondrial DNA analysis is the method of choice when dealing with environmentally challenged samples, e.g. identification of mass disaster victims, exhumed human remains.