DNA Casework

Evidence Containing Blood

The DNA Casework section of the Missouri State Highway Patrol Crime Laboratory work cases involving homicide, sexual assault, burglary, assault, and missing persons. The section is assingned the tasks of locating and identifying biological fluids from crime scene evidence. Once the biological fluids have been identified the analysts will then genetically type the evidence sample.

Typical piece of evidence containing blood

Deoxyribonucleic Acid or DNA has become a very useful crime fighting tool. The Laboratory began using the Polymerase Chain Reaction (PCR) in 1995. The most recent use of the PCR is the application of STR's or Short Tandem Repeats, which the Patrol started using in 1999 and is still using today. The PCR technology has enabled analysts to obtain DNA profiles from old evidence and evidence that only contains a small quantity of DNA. The laboratory has also implemented the use of Y-STR. DNA from the Y chromosome is specific to the paternal blood line. While Y-STR cannot identify a specific individual it is useful in discerning mixtures and in instances in which a limited amount of STR data is available.

Crime scene evidence is submitted to the laboratory from law enforcement agencies throughout the state. The analysts in the DNA casework section have the capabilities of identifying semen and human blood. While DNA can be obtained from saliva, vaginal secretions and skin cells the analysts cannot identify these items prior to DNA analysis.

The laboratory uses capillary electrophoresis and computer equipment to generate DNA profiles. The Genetic Analyzer detects the repeat sequences and uses an attached computer to compare the repeat sequences to known DNA sequences to generate a profile, which displays as peaks on the computer screen. Analysts have the option of using a 310 Genetic Analyzer which contains just 1 capillary or a 3130 Genetic Analyzer which contains 4 capillaries.

310 Genetic Analyzer

310 Genetic Analyzer

DNA profiles are developed from crime scene samples and known reference sample from individuals associated with a crime. Known reference samples are required for comparison because the DNA profile that is developed gives limited information about the individual who deposited the DNA. Known reference samples can be provided by law enforcement in the form of a buccal standard, a swab taken from inside the mouth, or a blood standard, in a purple cap blood tube.

DNA Profiles

Example of DNA Profiles

In recent years the laboratory has purchased two different types of robotic systems. The robotics will assist analysts in extracting the DNA from the evidence items for future genetic typing.

Maxwell 16 Robot

Maxwell 16 Robot

The DNA casework section participates in the COmbined DNA Index System (CODIS). CODIS is a DNA Database containing thousands of DNA profiles from convicted offenders, crime scene samples, samples from families of missing persons and unidentified human remains. The CODIS database enables state and local crime laboratories to exchange and compare DNA profiles electronically. CODIS is a very useful tool in solving cases that do not contain suspects and connecting multiple crimes to a single individual.