Assessment of IrisPlex-based multiplex for eye and skin color prediction with application to a Portuguese population
DNA phenotyping research is one of the most emergent areas of forensic genetics. Predictions of externally visible characteristics are possible through analysis of single nucleotide polymorphisms. These tools can provide police with “intelligence” in cases where there are no obvious suspects and unknown biological samples found at the crime scene do not result in any criminal DNA database hits. IrisPlex, an eye color prediction assay, revealed high prediction rates for blue and brown eye color in European populations. However, this is less predictive in some non-European populations, probably due to admixing. When compared to other European countries, Portugal has a relatively admixed population, resulting from a genetic influx derived from its proximity to and historical relations with numerous African territories. The aim of this work was to evaluate the utility of IrisPlex in the Portuguese population. Furthermore, the possibility of supplementing this multiplex with additional markers to also achieve skin color prediction within this population was evaluated. For that, IrisPlex was augmented with additional SNP loci. Eye and skin color prediction was estimated using the multinomial logistic regression and binomial logistic regression models, respectively. The results demonstrated eye color prediction accuracies of the IrisPlex system of 90 and 60 % for brown and blue eye color, respectively, and 77 % for intermediate eye color, after allele frequency adjustment. With regard to skin color, it was possible to achieve a prediction accuracy of 93 %. In the future, phenotypic determination multiplexes must include additional loci to permit skin color prediction as presented in this study as this can be an advantageous tool for forensic investigation.
KeywordsEye color prediction Skin color prediction EVC Forensic DNA phenotyping IrisPlex Multinomial logistic regression
The authors would like to express their sincere gratitude to all the volunteers who contributed to this work by providing samples. The authors would also like to thank two anonymous reviewers who gave valuable comments and advice on how to improve the content of this article.
Conflict of interest
The authors declare that they have no conflict of interest.
All experiments were approved by the Governing board of the National Institute of Legal Medicine and Forensic Sciences, Portugal.
- 11.(2004) Scientific Working Group on DNA analysis methods, revised validation guidelines. Forensic Sci. Commun. 6Google Scholar
- 17.Kennedy H (1996) Muslim Spain and Portugal. A Political History of al-Andalus. LongmanGoogle Scholar
- 18.Pinto AC, Lloyd-Jones S (2003) The last empire: thirty years of Portuguese decolonization. ix, 156 pGoogle Scholar
- 39.Croissant Y (2013) mlogit: multinomial logit model. R packageGoogle Scholar
- 40.R Core Team (2014) R: A language and environment for statistical computingGoogle Scholar
- 42.Ferri C, Hernández-Orallo J, Salido M (2003) Volume under the ROC Surface for Multi-class Problems. In: Lavrač N, Gamberger D, Blockeel H, Todorovski L (eds) Mach. Learn. ECML 2003 SE - 12. Springer Berlin Heidelberg, pp 108–120Google Scholar
- 44.Hilbe JM (2009) Logistic regression models. Chapman & Hall/CRC Press, Boca RatonGoogle Scholar