The introduction of DNA as evidence in the court system in the mid-1980s revolutionized forensic science resulting in thousands of new convictions, but also, at the same time, hundreds of acquittals of convicted persons throughout the world, and the elucidation of many cases of disputed paternity. However, arguing that DNA analyses are perfect and infallible is wrong.
The regular analysis image of a sample must be a series of peaks, which correspond to the number of repeated elements in the area of DNA that gets hyper-multiplied. Due to the fact that the number of repetitions of these elements will vary from person to person, we have the ability to identify the origin of the genetic material available. The number and the identity of these polymorphic areas depends on the genome of the given individual (genetic background or parental relationship), and the quantity and quality of the material being analyzed. Usually in Europe, in cases of identification, 12-16 polymorphic systems are analyzed (Extended European Standard Set) and in case of doubt, five more systems and some polymorphisms in the Y chromosome (men) are analyzed.
The result of the analysis becomes very complicated when there is a mixture of genetic material from more than one person, which in criminology and forensics is very common. In the analysis and interpretation of the results from such a mixed or incomplete sample is where the subjective opinion of each biologist conducting the analysis of the sample can creep in.
In a renown example (New Scientist, Aug. 2010) after a trial and conviction of a man for rape based on the findings from a mixture of genetic material, the analyst’s findings were given to 17 independent biologists, in accredited USA medical facilities, without any further knowledge of the case or the data they analyzed. Only one replied that he could not exclude the guilt of the accused, four that needed further analysis (undecided) and 12 of the 17 that ruled out the possibility of the accused being guilty! If the DNA analysis was entirely objective, as advertised, all 17 biologist should have reached the same conclusion.
We must therefore realize that DNA analysis, like all forensic analyzes, includes some subjectivity, and that is likely that personal bias may affect the judgment and decisions of the scientist conducting the analysis.
The problem with the subjective interpretation of results is further magnified by differences in the analysis procedure among different laboratories. Many laboratories have set a minimum detection limit, above which a top is accepted as a real allele, compared with the “noise” of the machine, while other laboratories depend on the analyst’s judgment. Of course there are some guidelines published by the scientific community (Scientific Working Group on DNA Analysis Methods, 2010) where the criteria to accept a top as a real allele are stated, along with the quantity and quality of genetic material which is the minimum acceptable sample for analysis, but these instructions are not required, nor does anyone monitor if they are uphold, especially among the non-accredited by the National Accreditation Council (ESYD) laboratories.
DNA analysis is undoubtedly a great tool in the hands of justice, as well as for the elucidation of questionable paternity cases, but one should always remember that good tools also need skilled operators in order to provide the desired results, and in this case, a correct, beyond any doubt, result.
Pantelis B. Konstantoulakis, BSc, PhD