DNA Databases

         DNA Databases
All DNA profiles stored in CODIS are generated using STR (short tandem repeat) analysis.CODIS utilizes computer software to automatically search its two indexes for matching DNA profiles. Law enforcement agencies at federal, state, and local levels take DNA from biological evidence (e.g., blood and saliva) gathered in crimes that have no suspect and compare it to the DNA in the profiles stored in the CODIS systems. If a match is made between a sample and a stored profile, CODIS can identify the perpetrator. This technology is authorized by the DNA Identification Act of 1994. All 50 states have laws requiring that DNA profiles of certain offenders be sent to CODIS. As of January 2003, the database contained more than a million DNA profiles in its Convicted Offender Index and about 48,000 DNA profiles collected from crime scenes but which have not been connected to a particular offender.

         Origin of mitochondrial DNA
As more offender DNA samples are collected and law enforcement becomes better trained and equipped to collect DNA samples at crime scenes, the backlog of samples awaiting testing throughout the criminal justice system has increased dramatically. In March 2003 President Bush proposed $1 billion in funding over 5 years to reduce the DNA testing backlog, build crime lab capacity, stimulate research and development, support training, protect the innocent, and identify missing persons. For more information, seethe U.S. Department of Justice's Advancing Justice Through DNA Technology. The primary concern is privacy. DNA profiles are different from fingerprints, which are useful only for identification.

         Deoxynucleic acid - DNA
DNA can provide insights into many intimate aspects of a person and their families including susceptibility to particular diseases, legitimacy of birth, and perhaps predispositions to certain behaviors and sexual orientation. This increases the potential for genetic discrimination by government, insurers, employers, schools, banks, and others.Collected samples are stored, and many state laws do not require the destruction of a DNA record or sample after a conviction has been overturned. So there is a chance that a person's entire genome may be available --criminal or otherwise. Although the DNA used is considered junk DNA STRs single tandem repeated DNA bases in the future this information may be found to reveal personal information such as susceptibilities to disease and certain behaviors. Who is chosen for sampling is also a concern. In the United Kingdom, for example, all suspects can be forced to provide a DNA sample. Likewise, all arrestees regardless of the degree of the charge and the possibility that they may not be convicted can be compelled to comply. This empowers police officers, rather than judges and juries, to provide the state with intimate evidence that could lead to investigative arrests.In the U.S arresting people on less than probable cause just to obtain DNA evidence raises the question of Fourth Amendment violations against unreasonable search and seizure. Practicality also is a concern. An enormous backlog of over half a million DNA samples waits to be entered into the CODIS system. The statute of limitations has expired in many cases where the evidence would have been useful for conviction . The term DNA fingerprinting was coined by British geneticist Alec Jeffreys only ten years ago. Since that time, DNA forensics has become an important tool in law enforcement.

In some cases the DNA tests have helped convict suspects, while in others the tests have exonerated suspects or overturned previous convictions. Recent high profile court cases have put the spotlight on DNA forensics and created the impression that there is a lack of agreement among the experts on the reliability of this evidence. I spoke with Dr. Bruce S. Weir, an expert witness for the prosecution in the OJ Simpson case, about the methods and controversies surrounding DNA evidence.First, let's begin with a basic question, what do we mean when we say DNA fingerprinting.DNA fingerprinting, or DNA profiling as I prefer to call it, characterizes a small portion of our DNA . It is a way of identifying the DNA content of an individual. We think of fingerprints as being unique to the individual. We know that even genetically identical twins have different fingerprints. In contrast, DNA typing, because it uses a very small fraction of the DNA, is certainly not unique.Let's imagine an hypothetical crime scene. When the technical people arrive at the crime scene, what do they do, what are they looking for The people at the crime scene look for biological tissues, such as blood stains on the ground and semen stains on clothing. They may take swabs from the victim's body if rape is involved. It is also possible to extract DNA from exotic things like the saliva on the back of a postage stamp. If it is a very old crime, they may obtain DNA samples from a skeleton.Wouldn't a drop of blood or other specimen at a crime scene be commingled with all kinds of other DNA from bacteria, flora etc How is this extraneous DNA excluded The methods used in forensic DNA are not so much concerned with excluding extraneous DNA as in identification of human DNA.

         Protein Synthesis
The probes used are very specific for human DNA. Tell us a bit about the techniques used in forensic DNA testing.. Are the laboratories using PCR to look at allele combinations or RFLP (restriction fragment length polymorphisms) or both? What are the advantages of the different techniques.The laboratories use both techniques. The RFLP tests were developed first and are better in the sense that they are much more variable. There are many more variants in the population. A typical RFLP will have 30 distinguishable types. The disadvantage of the RFLP method is that it requires a relatively large amount of DNA along with radioactive labeling visualized on a gel. To expose an X-ray film with a radioactive labeled probe takes about a week. You have to do that for each system, so the entire process can take many weeks. PCR techniques offer the advantage of requiring only trace amounts of DNA and they can be done overnight. Unfortunately, PCR systems currently in use are not very variable, allowing typically only three of four variants.When laboratories use RFLP they are only looking for five orsix polymorphisms. Why not look for ten or 100 or 1000.The State of N. Carolina uses eight polymorphisms. I believe by the time you have eight systems even with as few as 20 alleles, you are not going to gain anything by looking for more.A number of statistical techniques are now used to confirm the reliability of these methods. Can you explain how the most fundamental technique, the allele multiplication rule, is used to rate the odds of a match between specimens.If we want to come up with a figure for the frequency of the pattern, we rely on statistical model. A DNA profile contains information from let's say five RFLPS or five PCRs. This provides at least ten pieces of information The entire profile has almost never been seen. 1