IOWA DIVISION OF CRIMINAL INVESTIGATION
CRIMINALISTICS LABORATORY
DNA PROFILING SECTION

The DNA Profiling Section provides examinations to law enforcement agencies at no cost. Items from criminal cases are examined for the presence of human DNA. DNA can be found in biological fluids, tissues and bones of the body. If DNA profiles are obtained from samples in question, comparisons may be made to known DNA profiles from individuals believed to be involved. The DNA Profiling Section also determines the DNA profiles of convicted offenders and stores their profiles in a computer database. Comparisons are made between the profiles found in the convicted offender database and the profiles obtained from criminal cases where no suspect has been identified.

What is DNA?

DNA is an acronym for the genetic material deoxyribonucleic acid. DNA is found in all nucleated cells of the body. The DNA humans receive from their parents is 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.

What is DNA testing?

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.

What can be tested?

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.

How should samples be collected?

All samples should be collected using appropriate collection procedures to avoid sample destruction or degradation. Biological material is best preserved in a dry, cold environment. All items should be packaged separately into paper bags or envelopes.

DNA Evidence Collection at Crime Scenes is a pdf file containing information from the Criminalistics laboratory regarding the collection of evidence.

For more information on collecting and packaging biological samples please visit the following website: http://www.fbi.gov/hq/lab/handbook/examlist.pdf

How should known reference samples be collected?

Known reference samples are most commonly submitted as either buccal swabs or as liquid blood samples. When possible, known reference samples should be provided at the same time as the questioned evidentiary material. 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 before packaging. 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 liquid blood sample should be collected by drawing blood (by qualified medical personnel) into two purple capped 5ml blood tubes. Gray capped tubes may also be used in the absence of purple capped tubes. Identify the blood sample with the appropriate information and submit it to the lab in a timely fashion. Liquid blood should be refrigerated and shipped in cold packs. Do not freeze or ship liquid blood in dry ice. Pack the blood tubes in Styrofoam with absorbent material surrounding the tubes.

What type of DNA test is performed?

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 fifteen 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.

How long will testing take?

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.

How specific are DNA "matches"?

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.

What can be done with mixtures of DNA from two or more people?

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.

Are samples consumed in the process of DNA testing?

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.

Should cases without suspects be submitted?

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 are placed into a computer database and searched against DNA profiles from convicted offenders as well as evidentiary samples from additional "No Suspect" cases.

What is CODIS?

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. As the number of profiles in convicted offender databases increases, the number of "cold hits" or matches to "No Suspect" cases increases. Currently, enormous backlogs of convicted offender samples are unanalyzed in the USA. Substantial reduction of these backlogs is expected in the next few years depending on available funding.

If you have any questions, please contact the Iowa Department of Public Safety, Division of Criminal Investigation, Criminalistics Laboratory at : (515) 725-1500