Abstract
Numerous major advances have been made in forensic genetics over the past decade. One recent field of research has been focused on the analysis of External Visible Characteristics (EVC) such as eye colour, hair colour (including hair greying), hair morphology, skin colour, freckles, facial morphology, high myopia, obesity, and adult height, with important repercussions in the forensic field. Its use could be especially useful in investigative cases where there are no potential suspects and no match between the evidence DNA sample under investigation and any genetic profiles entered into criminal databases. The present review represents the current state of knowledge of SNPs (Single Nucleotide Polymorphisms) regarding visible characteristics, including the latest research progress in identifying new genetic markers, their most promising applications in the forensic field and the implications for police investigations. The applicability of these techniques to concrete cases has stoked a heated debate in the literature on the ethical implications of using these predictive tools for visible traits.
Highlights
Introductionsingle nucleotide polymorphisms (SNPs) possess several characteristics that make them more valuable markers than short tandem repeats (STRs): smaller amplicon size (50–150 bp); higher occurrence in human genome (approximately 1 in every 1000 bp, millions per individual, representing the most common human genetic variation); lower mutation rate; and an elevated amenability to high-throughput genotyping through multiplexed sequencing [1, 5, 7, 9,10,11,12]
single nucleotide polymorphisms (SNPs) possess several characteristics that make them more valuable markers than short tandem repeats (STRs): smaller amplicon size (50–150 bp); higher occurrence in human genome; lower mutation rate; and an elevated amenability to high-throughput genotyping through multiplexed sequencing [1, 5, 7, 9,10,11,12]
The following external visible characteristics (EVC) have been evaluated for forensic DNA phenotyping: hair colour, eye colour, skin colour, hair morphology, height, weight, facial morphology, presence of freckles, male-pattern baldness, and myopia
Summary
SNPs possess several characteristics that make them more valuable markers than STRs: smaller amplicon size (50–150 bp); higher occurrence in human genome (approximately 1 in every 1000 bp, millions per individual, representing the most common human genetic variation); lower mutation rate; and an elevated amenability to high-throughput genotyping through multiplexed sequencing [1, 5, 7, 9,10,11,12] These features make SNPs suitable for obtaining information in cases of aged, degraded/or low copy biological samples, (where DNA fragments may be smaller than the required length for STR analysis), in kinship and paternity testing (especially in cases where relationships are generations apart) and in population and evolutionary genetics research [4, 11, 12]. The VISAGE consortium has recently suggested, at least for the use of MLR (multinomial logistic regression) as the most appropriate method for predicting appearance traits from DNA, especially with regard to hair, eye and skin prediction [20]
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