DNA-based prediction of human externally visible characteristics in forensics: Motivations, scientific challenges, and ethical considerations☆
Section snippets
Forensic motivations for DNA-based prediction of externally visible characteristics
The current use of human DNA in the forensic context, i.e. for the purpose of individual identification relies strictly on comparative grounds: DNA profiles obtained from crime scene material are compared with those of known potential suspects. Similarly, in mass disaster or missing person cases, DNA profiles obtained from an unknown person are compared with those of known potential relatives, or with direct reference samples from items belonging to the missing person [1]. If matches between
Challenges in finding reliable genetic predictors of externally visible characteristics
Recent technological advances in microarray-based genotyping technologies, allowing parallel testing of up to over one million of genetic markers (usually single nucleotide polymorphisms, SNPs), together with theoretical advancement in association testing have provided powerful tools to find genes involved in complex including some EVC traits [7], [8]. Complex traits are defined as phenotypic characteristics that are influenced by several genetic and additionally by environmental factors.
Externally visible characteristics with promising expectation for accurate DNA prediction
The EVC that so far is most accurately predictable with DNA markers is human gender or sex. A length difference between the X-chromosomal and the Y-chromosomal copy of the amelogenin gene is useful for DNA-based sex determination [12], and this marker is included in most of the commercially available kits used for human identity testing in forensics. However, this prediction test is not error-free, and some males are wrongly diagnosed as females simply because they carry a Y-chromosomal
Externally visible characteristics with less promising expectation for reliable prediction
While iris color represents a limited complex trait with one major genetic factor (HERC2/OCA2, at least for blue and brown colors), and only a few additional minor genetic factors, human adult body height (or stature) turned out to be an EVC with much higher complexity. It would be desirable for forensic applications if one could accurately predict human body height from DNA samples since adult body height varies considerably within and between human populations. The amount of heritability of
Ethical and legal considerations for DNA-based prediction of externally visible characteristics in forensics
In most countries, the prediction of EVCs in forensic DNA analysis will add a new qualitative dimension to criminal investigations, since so far DNA evidence in forensics is only used quantitatively. With the notable exception of the Netherlands, where the use of DNA markers for EVC prediction (including prediction of geographic origin) is allowed and regulated by a law adaptation in 2003, no other country has introduced specific laws that would allow using this type of evidence in casework (as
Conclusions
Genetic (e.g. DNA-based) prediction of externally visible characteristics of an unknown person who left a DNA sample at a crime scene (or from an unidentified body) is expected to be useful for police investigation to reduce the number of possible suspects if no direct suspects can be identified by conventional means of investigations. Since externally visible traits of a person are known to everybody who has ever seen this person before, they cannot be considered as private information.
Acknowledgements
We thank Kaye Ballantyne for useful comments on the manuscript. The original research of M.K. on the genetic basis of human visible traits and their prediction mentioned in this article is supported by funds from the Netherlands Forensic Institute (NFI), the Erasmus University Medical Center Rotterdam, and by a grant from the Netherlands Genomics Initiative/Netherlands Organization for Scientific Research (NWO) within the framework of the Forensic Genomics Consortium Netherlands.
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Paper based on two presentations at the DNA in Forensics meeting, Ancona, 27–30 May 2008.