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Biology & DNA

Spermatozoa Under Magnification
Spermatozoa Under Magnification

The Michigan State Police Biology Unit is primarily comprised of two sub-disciplines: Body Fluid Identification (BFI) and DNA Analysis. All evidence submitted to a forensic laboratory is initially screened for the possible presence of body fluids. This may be accomplished at any of our seven regional laboratories. If BFI analysis indicates the possible presence of biological material and the source of these fluids is in question, the item may be sampled and forwarded for subsequent DNA testing at the Grand Rapids, Lansing or Northville laboratory.

Body Fluid Identification (BFI) is best described as the examination of evidentiary items for the possible presence of bodily fluids. Items routinely submitted for BFI screening may include sexual assault evidence collection kits, bedding, swabs, clothing, tools, firearms, masks and shoes. The body fluids typically tested for include blood, semen, seminal fluid, saliva, urine, feces, hair characterization and cellular material. The techniques used to locate and characterize these body fluids include direct observation, microscopic examination, colorimetric chemical tests and immunological assays. Results obtained from BFI screening may help establish elements of a crime and suitability for subsequent DNA testing.

Examiner Processing Samples
Examiner Processing Samples

DNA analysis is a multi-step process that utilizes the most current methods and equipment available to obtain reliable results, even with low level samples. The Biology Unit uses a variety of extraction techniques to remove DNA from supporting substrates. This is followed by quantitative PCR using the qPCR and Plexor HY™ chemistry to determine if human and/or male DNA was recovered. The actual DNA typing of each sample is achieved through amplification of 16 genetic markers using the PowerPlex™ 16 HS short tandem repeat chemistry. The results of the amplification step are visualized with capillary electrophoresis genetic analyzers. When interpretable results are obtained, the DNA data are interpreted and compared to reference DNA profiles for potential inclusions or exclusions.

Required DNA Markers
Required DNA Markers

An additional technology termed Y-STRs is now being offered by the MSP. Y-STRs are technologically similar to standard DNA testing. However, Y-STRs target specific genetic markers present only on the male (Y) chromosome. Y-STRs are primarily used in the following situations:

  • Violent crimes (sex assaults and homicides)
  • Standard STR testing was unable to detect a male component
  • Suspect is known
  • Predominance of female DNA with a limited amount of male DNA (i.e. vaginal swabs)