How does it work?

There are millions of base pairs in each person's DNA that every person has a different sequence. Using these sequences, every person could be identified individually by the sequence of their base pairs. However, because there are so many millions of base pairs, the task would be very time- consuming. Instead, scientists are able to use a shorter method, because of repeating patterns in DNA.

Forensics and DNA: Applications

Biological Evidence 

DNA fingerprints are used to link suspects to biological evidence - blood or semen stains, hair, or items of clothing - found at the scene of a crime .Since its invention, hundreds of cases have been decided with the assistance of DNA fingerprint evidence  .Another important use of DNA fingerprints in the court system is to establish paternity in custody and child support litigation. In these applications, DNA fingerprints bring an unprecedented, nearly perfect accuracy to the determination.

Personal Identification

Because every organ or tissue of an individual contains the same DNA fingerprint, The DNA method is far superior to dental records, and blood typing strategies currently in use.

What are some of the DNA technologies used in forensic investigations? 

Restriction Fragment Length Polymorphism (RFLP) RFLP is a technique for analyzing the variable lengths of DNA fragments  that result from digesting a DNA sample with a special kind of enzyme. This enzyme, a restriction endo-nuclease, cuts DNA at a specific sequence pattern know as a restriction endo-nuclease recognition site. RFLP was one of the first applications of DNA analysis to forensic investigation.

PCR: Polymerase chain reaction (PCR) is used to make millions of exact copies of DNA from a biological sample. DNA amplification with PCR allows DNA analysis on biological samples as small as a few skin cells  .

STR Analysis : Short tandem repeat (STR) technology is used to evaluate specific regions (loci) within nuclear DNA. Variability in STR regions can be used to distinguish one DNA profile from another.

Mitochondrial DNA Analysis: Mitochondrial DNA analysis (mtDNA) can be used to examine the DNA from samples that cannot be analyzed by RFLP or STR. Nuclear DNA must be extracted from samples for use in RFLP, PCR, and STR; however, mtDNA analysis uses DNA extracted from another cellular organelle called a mitochondrion  .All mothers have the same mitochondrial DNA as their offspring. This is because the mitochondria of each new embryo comes from the mother's egg cell. The father's sperm contributes only nuclear DNA. Comparing the mtDNA profile of unidentified remains with the profile of a potential maternal relative can be an important technique in missing-person investigations.

Y-Chromosome Analysis: The Y chromosome is passed directly from father to son, so analysis of genetic markers on the Y chromosome is especially useful for tracing relationships among males or for analyzing biological evidence involving multiple male contributors.

Applications of DNA Fingerprinting: DNA fingerprinting is used in a variety of applications. It Can be used to solve Sexual assault and rape cases: scientists only had to match the DNA of the semen found at the scene of the crime with the DNA of any potential suspect to determine who was guilty of committed the crime. A DNA sample from the rapist could be obtained from a simple vaginal swab from the victim or any other semen that was released in the area  Paternity and maternity Testing The most frequent use of DNA testing is paternity and maternity testing .This name is somewhat misleading as almost any familial relationship can be tested to see if two people are related, not just parents and offspring .The most common use in this category is to determine who is the father and  mother of a particular child. There are two types of paternity testing; the first is prenatal testing, which is done before the child is born. The second is postnatal testing, done after the child is born.