DNA CASEWORK SECTION
The DNA Section consists of two units. They are as follows:
Frequently Asked Questions on DNA:
DNA is an acronym for the genetic material deoxyribonucleic acid. DNA is used by the body to determine whom an individual is, everything from physical features to personality. DNA is found in all nucleated cells of the body. One half of a person’s DNA comes from their mother and the other their father. This combination is what makes an individual unique with the exception of identical twins. The DNA found in an individual's blood is the same DNA that is found in their saliva, tissue, bone, etc.
DNA testing or "profiling" is used to identify a potential source of biological evidence by matching questioned samples (left at crime scenes) with known samples from victims and suspects. For example, when a sexual assault occurs and seminal fluid is left on the vaginal samples of the victim, it is possible to compare the DNA profile obtained from the semen donor to a known DNA profile from a suspect. Since the DNA profile from the suspect's semen will be the same as that of his known saliva or blood, a match will link a suspect to a crime.
Blood and semen are most commonly tested but they are not the only possible sources of DNA. Saliva, sweat, vaginal fluid, hair (with suitable root structure), muscle tissue and bone may also be tested. Urine and fecal samples may contain small quantities of DNA but are poor sources for testing.
All samples should be collected using appropriate collection procedures to avoid sample destruction or degradation. Additionally, every precaution should be taken to avoid contaminating the biological sample upon collection. Biological material is best preserved in a dry, cold environment. All items should be packaged separately into paper bags or envelopes.
For more information on collecting and packaging biological samples please go to the FBI website to access their Handbook of Forensic Services.
Known reference samples are most commonly submitted as either buccal swabs or as dried blood samples. When possible, known reference samples should be provided at the same time as the questioned evidentiary material. (Submitting agencies, please state on the case submission form if no known suspect sample is available and why.) Buccal swab(s) should be collected by scrubbing a clean and dry cotton swab on the inside surface of the cheek and gums. It is advisable to collect at least two swabs and to allow the swabs to air dry in a breathable swab box, paper envelope, or appropriate container. Identify the buccal swabs with the appropriate information and submit them to the lab in a timely fashion. The dry buccal swab does not need to be refrigerated. The known dried blood sample should be collected by drawing blood (by qualified medical personnel) on to a filter paper card using a finger stick collection device and having the blood sample blotted off the fingertip on to an appropriate filter paper card and air dried. Place the dried blood card into a paper envelope and seal. Identify the blood sample with the appropriate information and add biological identifier/hazard labels as appropriate. The dried blood sample does not need to be refrigerated. S ubmit the sample to the lab in a timely fashion.
Nuclear DNA testing is the method utilized by the Iowa DCI Crime Lab. Meaning that the DNA used for testing is found in the nucleus of a cell. The technique used to profile the DNA is called the Polymerase Chain Reaction (PCR). PCR allows millions of copies of very specific areas on the DNA molecule to be obtained. This process known as "amplification" is a powerful scientific tool because it allows very tiny amounts of DNA (which may have been left behind as evidence of a crime) to be successfully analyzed. Commercially purchased DNA typing kits are used to analyze as many as twenty three Short Tandem Repeats (STRs). STRs are genetic markers that vary in size among individuals. Their small size (typically 4 bases per repeat) makes them excellent for use with PCR and also makes them less susceptible to degradation. The STR tests are currently the most widely used DNA tests in the forensic community.
DNA testing involves a series of steps. First the item is examined for biological fluid stains or other possible sources of DNA. Once a source is found it is identified as seminal fluid, blood, etc. The DNA is then extracted from the sample, quantified, subjected to PCR and profiled using automated instrumentation. This process is greatly affected by the number of samples that need to be tested. In general, PCR testing can be completed within one month after a case is started, however, current backlogs may make this turn-around time longer.
STR matches are very discriminating for single-source samples. Typically, a complete DNA profile is estimated to occur in less than one out of one hundred billion random, unrelated people. In cases where complete DNA profiles cannot be obtained, the profile's frequency of occurrence becomes more common.
This situation is commonly encountered with sexual assault evidence. DNA extraction procedures are used to separate sperm cell DNA from non-sperm cell DNA. In many cases this is successful and a clear profile of the perpetrator can be obtained. Sometimes complete separation cannot be obtained and the perpetrator's sperm cell DNA will be mixed with the victim's DNA. Blood-blood and semen-semen DNA mixtures can also occur. The ability to distinguish individual contributors to a mixed DNA profile will vary from case to case, and is highly dependent upon the relative quantity of DNA contributed to the mixture by each individual.
The amount of sample that is required for testing is minimal, so typically only a small fraction of larger sized stains are consumed by testing. This allows independent testing to be performed should the defendant(s) choose to do so. When insufficient sample is available for independent testing the extracted DNA will be stored at the crime lab.
Yes. "No Suspect" crimes against persons should be submitted for testing. In many cases DNA evidence left at the scene may be the only link to potential perpetrators. The DNA profiles obtained from "No Suspect" cases may be placed into a computer database and searched against DNA profiles from convicted offenders as well as evidentiary samples from additional "No Suspect" cases. Submitting agencies, please state on the case submission form if “no suspect is identified”.
The Federal Bureau of Investigation facilitates the use of a national DNA database called CODIS. CODIS is an acronym for the Combined DNA Indexing System. It may be utilized for DNA profile searches within the state of Iowa as well as across the United States.
A DNA profile becomes CODIS eligible when it is obtained from biological material collected from a crime scene and is attributable to a presumed perpetrator.
Additionally, please describe any known relationships between the victim and suspect (husband/wife, boyfriend/girlfriend, etc). Submitting agencies are encouraged to provide this information in the "Case Comments" section of the pre log.
Please be aware that some items submitted for DNA testing may not be eligible for entry into CODIS. To become eligible for CODIS an item must be collected from a crime scene and also be attributable to a presumed perpetrator. The following are examples of submitted items that would not be eligible for CODIS:
If you have a question that was not answered in the above FAQ, please contact the Iowa Department of Public Safety, Division of Criminal Investigation, Criminalistics Laboratory at (515) 725-1500.
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