Frequently Asked Questions
General Questions About DNA:
1. What is DNA? DNA stands for deoxyribonucleic acid. It is found in all living things. DNA is an ‘instruction manual’ for life. It is also the hereditary or genetic material. Humans inherit half of their DNA from their mother and half from their father. We all have similar DNA content, because it is what makes us human. However, with the exception of identical twins, no two humans have identical DNA.
2. Where is DNA found in the body? DNA is found within cells (e.g. white blood cells, sperm cells, cells lining body cavities, skin cells) in the human body. Most of the DNA is found in the nucleus or ‘brain’ of the cell. This type of DNA is known as nuclear DNA. A small amount of DNA is found in another part of the cell known as a mitochondrion. This type of DNA is known as mitochondrial DNA.
3. Why would mitochondrial DNA analysis be used instead of nuclear DNA analysis? Most samples encountered in forensic science have sufficient nuclear DNA for analysis. Common examples are blood, semen, saliva, and hair roots. There are certain types of samples such as hair shafts that do not contain nuclear DNA that can be analyzed. The mitochondrial DNA in the hair shaft is typically analyzed. Sometimes, the nuclear DNA present in samples is destroyed by environmental conditions (e.g. heat and moisture). Because there are many more copies of mitochondrial DNA than nuclear DNA in a cell, enough mitochondrial DNA may remain for analysis, even though the nuclear DNA has been destroyed. Mitochondrial DNA analysis was critical in the identification of human remains from the World Trade Center tragedy on September 11, 2001.
4. What types of forensic samples can be submitted for DNA analysis? Typical samples are bloodstains, vaginal swabs, oral swabs, rectal swabs, penile swabs, breast swabs, semen stains, cigarette butts, bones, hairs, etc. Due to the excellent sensitivity of current testing methods, even items such as chewing gum, sunflower seeds, toothbrushes, ski masks, swabs from steering wheels, beverage cans, and perspiration from clothing can be successfully analyzed. Modern crime scene investigation demands personnel recognize that almost any type of evidence can potentially be valuable for DNA analysis.
5. Why are there so many headlines about problems with DNA testing laboratories? The science behind forensic DNA analysis has been proven to be sound. It must, however be remembered that it is a very human-intensive activity. Proper training is critical to the quality of the results. As the popularity of DNA analysis increases, there is more pressure on laboratories to analyze greater numbers of samples. In some instances training programs are insufficient, and laboratory checks and balances are not as strict as they should be.
Questions for Defense Attorneys:
1. How do I go about discovering more about your case review services? Contact our laboratory to discuss your case. We will discuss your case with you (free of charge) and provide solutions for you to consider. If you are interested in going further, we would need to see copies of all relevant reports issued by the testing laboratory in order to provide you with a cost estimate for a thorough review of the DNA testing results. The estimate will be contained in a letter explaining our service provisions. As soon as you decide to retain our services, we will provide you with a list of items needed for discovery.
2. Is it better to have DNA samples re-analyzed to verify results or have all testing records and results reviewed by an expert? This question has to be answered on a case-by-case basis. Interpretation of results tends to be the most challenging (and therefore most prone to errors) portion of the DNA analysis procedure. For this reason, it is often a better use of resources to have an expert review the work that has already been completed. However, sometimes it is advisable to have samples analyzed that were not considered by the original testing laboratory. If there are questions about a possible sample mix-up, actual sample re-analysis would be appropriate.
3. I’ve heard that DNA evidence is essentially infallible, how can you possibly help my defense? First and foremost, we will help you understand exactly what the DNA testing results mean. Crime laboratory reports can be very difficult to comprehend for the non-scientist. Although the scientific basis of DNA testing is now extremely well-established, the testing is performed by human beings who are not infallible. Our review process assesses: the training and qualifications of the DNA analyst, the adequacy of the laboratory notes, the selection of samples and testing procedures, the use of appropriate quality control measures, adherence to protocols, legitimacy of results, and soundness of conclusions.