DNA

Core activities

Stated below is the description of the field of expertise DNA – Source level.

In a criminal law context, experts working in the field of DNA – Source level, primarily seek to answer question 2 'From whom does the biological trace originate? In other words, who is the donor of the cellular material?'

The DNA - Source level expert subjects the biological trace material to (Autosomal and/or Y–chromosomal) DNA analysis, and may subsequently perform DNA profile comparison. To do this, the expert compares DNA profiles from trace material with each other and/or with DNA profiles from reference samples.

In addition, comparisons may be made with DNA profiles in DNA databases.

The DNA - Source level expert is concerned with interpreting and comparing individual and complex and/or mixed DNA profiles obtained from the trace material under standard conditions or with the help of low template/minimal traces DNA techniques. The expert’s focus is on the whole scope of biological traces, including contact traces.

The tasks that fall within the field of DNA - Source level are:

  • Detection and identification of bodily fluids by means of visual examination and presumptive biochemical test methods, followed up by confirmation of the search result by means of microscopy and immunoassay.
  • Autosomal DNA analysis and interpretation.
  • Low template/minimal traces DNA analysis and interpretation.
  • Statistical calculations to determine the evidential value of a match.

Experts within the field of DNA - Source level are capable of applying Autosomal and Low Template/Minimal Traces DNA analysis techniques and are capable of interpreting, statistically evaluating and reporting on the results of these techniques.

Experts within the field of DNA - Source level are capable of applying DNA techniques used to answer question 1 'Are biological materials present on the exhibit and what is the nature of the cellular material in the biological trace?' even though not all DNA experts perform these analyses (anymore) themselves.

Experts within the field of DNA - Source level do not have to be able to answer question 3. 'How was the biological material deposited?'. Being able to answer this question adequately is central to reporting at Activity level and requires specialised knowledge and expertise.

Bounderies of the field of expertise

Within the practice of DNA - Source level, five specific types of questions exist that require additional expertise and experience, and therefore, fall outside the scope of DNA - Source level as registered by the NRGD:

  • Y-chromosomal DNA Testing
    Specific question: Subject biological trace material to Y chromosomal (Y-STR) DNA Testing and then carry out comparative Y chromosomal DNA analysis including interpretation.
  • Kinship DNA Testing
    Specific question: Investigate a (presumed) biological relationship based on DNA profiles of individuals and/or traces.
  • Externally Visible Characteristics
    Specific question: Determine the geographical origin and/or externally visible characteristics of the unknown cell donor (the possible perpetrator of the crime) by means of DNA analysis of the trace evidence.
  • Mitochondrial DNA Testing
    Specific question: Subject biological trace material to Mitochondrial DNA Testing and then carry out comparative Mitochondrial DNA Testing.
  • Reporting at Activity level
    Specific question: How was the biological material deposited? (see above).

When reporting as an expert registered for the field of DNA - Source level, the expert should be aware of the possibilities and limitations of the above mentioned techniques and/or specialisations, and in addition, the expert should be aware of the potential for international searches of intelligence databases and of new developments such as RNA, SNPs and Next Generation Sequencing. The expert should also be aware of the pros and cons of these techniques, specialisations and/or developments.