DNA typing is the modern, much publicized method through which scientists in a court of law can use DNA samples like a fingerprint to catch a criminal or find a child's father. Because each of us has our own unique genetic sequence, DNA can provide a means of identification accurate enough to be used in the courtroom. In a murder case, for example, if a suspect is discovered to have clothes stained with blood containing the DNA of the victim, the case against him or her could be made much stronger.

The process of DNA typing is the careful study of restriction fragment length polymorphisms (RFLPs for short). Though much of the genetic information that every human has is identical from one person to the next, there are some segments that vary- these are the RFLPs, and these are the segments useful in identification. For a segment to be considered an RFLP it must meet three requirements:

1. It must differ from person to person
2. It must follow Mendel's laws
3. It must have a low mutation rate

The process of DNA typing is a long one, and first the sample must be prepared. The DNA is put into a special fluid, and then separated from it again multiple times to purify the sample. Then enzymes are added and the mixture is heated so that the molecules are cut into separate RFLP segments. These pieces are then mixed with a gel and an electrical current is applied. This process, called gel electrophoresis, causes the naturally charged DNA segments to sort themselves by size. Once this is complete, the RFLPs are transferred from the gel to a solid membrane, usually nylon fiber, to create what is called a Southern blot (named after the scientist who discovered the process). The RFLPs have been sorted, but they are still invisible, so the next step is to make them visible through radioactive probe binding. Special radioactive DNA segments are prepared and added to the blot so that they connect to the RFLPs through normal base pair rules. The blot is then exposed to delicate x-ray film for a few days at very low temperatures. This film detects the position of the radioactive probes, and therefor the RFLPs themselves. The final product is an autoradiograph with a unique pattern of sorted RFLP segments.

Uses
The use of DNA typing to find a person's parent depends on the idea that an individual's genes must come from either their mother or their father without too much mutation. Since this seems to be the case, this method has been used to sort out switched baby cases and the like.

In the criminal courtroom, traces of DNA left at a crime scene can often prove to be crucial evidence. Blood stains on suspects can be matched to victims and vice-versa. Enough genetic information to complete the identification process can be found in any body cell left behind, regardless of its origins- blood, saliva, semen, hair, etc. The accuracy of DNA typing is so extreme that it has generally become a valid tool to use even in the highest-pressure cases, though some still distrust its abilities and argue against its use.