Quantifying Human DNA

DNA/Serology

The Michigan State Police Forensic Science Division has six laboratories with biology units. These units are located in Bridgeport, Grayling, Grand Rapids, Lansing, Northville, and Sterling Heights. Of these six laboratories, Grand Rapids, Lansing, and Northville offer DNA analyses. DNA is the same for every cell, tissue, and organ of a person. Consequently, DNA has become a primary method of identifying and distinguishing amongst individuals.

                                                                                                                       Preparing Samples for the ABI

                                                                                                                        310 Genetic Analyzer

The analysts in the Biology Unit routinely examine evidentiary items for the presence of blood and body fluids. The analyst begins by evaluating the available evidence that may help establish that a crime has been committed, link a suspect or victim to a crime, or exonerate a suspect. Initially, items of physical evidence are examined for physiological fluids such as blood, semen, or saliva. The questioned stains are first identified as to the type of stain present. Additional analyses may be performed depending upon investigating officer's request, case circumstances, sample size, and condition.

          ABI Genetic Analyzer

The Lansing Laboratory first reported DNA cases in 1991 using Restriction Fragment Length Polymorphism (RFLP) analyses. The

Grand Rapids and Northville Laboratories began reporting DNA cases in 1999. The three DNA laboratories now perform Short Tandem Repeat (STR) analysis using capillary electrophoresis (CE). Capillary electrophoresis allows analysts to look at 13 different loci as well as a gender determinant in a short period of time. Using this technology, the probability of matching an individual at random (other than an identical twin) is generally measured in terms greater than one in a quadrillion.

In cases where a suspect has not been identified, the DNA profile obtained from evidentiary items can be entered into the Combined DNA Index System (CODIS) which is administered by the F.B.I. The CODIS system enables federal, state, and local crime laboratories to exchange and compare DNA profiles electronically. This allows for possible DNA matches to convicted felons nationwide as well as linking serial cases.