Study of genetic markers with medico-legal and forensic interest in Lisbon’s population (preliminary results)

Abstract

Across Portuguese laboratories of forensic genetics, the 13 STRs from the CODIS system and at least four more STR’s (D2S1338, D19S433, Penta D and Penta E) are analyzed. Nevertheless, in complex cases it could be necessary the study of additional genetic markers.

Given the lack of population studies regarding 10 new STR - D2S1360, D3S1744, D4S2366, D5S2500, D6S474, D7S1517, D8S1132, D10S2325, D12S391, D21S2055 -, it’s necessary to study their frequencies in Lisbon’s population. In this study, samples from 176 individuals, from both genders and from unrelated individuals comprised in forensic investigations in progress at Instituto Nacional De Medicina Legal e Ciências Forenses (INMLCF), were analyzed with the Investigator HDplex Kit (Qiagen).

Allele frequencies and statistical parameters were estimated with Arlequin 3.5.2.2 and PowerStat V12.

The obtained results for forensic statistical parameters, such as observed and expected heterozygosity, polymorphism information content, power of discrimination, based on single allele frequencies reveal that the Investigator HDplex Kit (Qiagen) is highly informative and can represent an important tool for genetic identification purposes for forensic investigations ongoing at the INMLCF, especially in paternity cases, related to individuals from the great Lisbon area.

Keywords1. Introduction

The population in this study is composed of individuals who were born and live in Lisbon and whose parents were also born in Lisbon.

Due to the lacking of population studies regarding the following new STRs (Short Tandem Repeats): D2S1360, D3S1744, D4S2366, D5S2500, D6S474, D7S1517, D8S1132, D10S2325, D12S391, D21S2055, it was necessary to evaluate their frequencies in Lisbon’s population.

Often, in complex cases, in order to confirm previously obtained results, the Investigator HDplex Kit (Qiagen) amplifies a set of STR markers, most of which are not featured in commonly used marker standards. This enables the reliable differentiation of forensic samples providing a heightened discriminatory power in these demanding cases.

The aim of this study is to analyze the frequencies of these additional STRs among Lisbon’s population.

The obtained results for forensic statistical parameters such as observed heterozygosity, polymorphism information content, power of discrimination and mean exclusion chance, based on single allele frequencies reveal that this system is highly informative and can represent an important tool for genetic identification purposes for forensic investigations ongoing on INMLCF, related to individuals from Lisbon.

2. Materials and methods

In this study, blood samples were analyzed from 176 unrelated and healthy individuals from ongoing investigations at the INMLCF.

The samples were randomly selected from both genders without restrictions regarding their ages.

The Chelex 100® method was used to extract the DNA from the selected samples, and then amplified using a 9700 Perkin Elmer (Applied Biosystems) thermocycler following the manufacturer instructions [[1]Walsh P.S. Metzger D.A. Higuchi R. Chelex100 as a medium for simple extraction of DNA for PCR- based from forensic material.].The amplified products were detected using an ABI PRISM® 3130 xl Genetic Analyzer (Applied Biosystems). The fragments were then typed with GeneMapper® ID (Table 1).

Table 1Allele frequencies for twelve autosomal STR from Lisbon’s population.

Allele frequencies and statistical parameters were estimated with Arlequin 3.5.2.2 software and PowerStats V12 [[2]Schneider, Arlequin (version 3.5.2.2): an integrated software package for population genetics data analysis.].3. ResultsAllele frequencies calculated for the analysed markers in Lisbon’s population and population statistics including Observed Heterozygosity (Ho), Expected Heterozygosity (He), Hardy-Weinberg (P), Matching Probability (MP), Power of Discrimination (PD), Polymorphic Information Content (PIC), Power of Exclusion (PE), Typical Paternity Index (TPI), Homozygotes (Hom), Heterozygotes (Het), are represented in Table 2.

Table 2Statistical parameters of forensic interest for 12 autosomal STR from Lisbon's population.

4. DiscussionAll the markers showed a high degree of genetic polymorphism, with He values ranging from 0.785 (D6S474) to 0.951 (SE33). Based on heterozygosity and polymorphic information, the SE33 locus is the most informative among the 12 STR loci. All the PD values were higher than 0.912, and PIC values were higher than 0.750 as seen in Table 2.

The obtained results for forensic statistical parameters, such as observed and expected heterozygosity, polymorphism information content, power of discrimination, based on single allele frequencies reveal that the Investigator HDplex Kit (Qiagen) is highly informative and can represent an important tool for genetic identification purposes for forensic investigations ongoing at the INMLCF.

Declaration of Competing Interest

None.

ReferencesWalsh P.S. Metzger D.A. Higuchi R.

Chelex100 as a medium for simple extraction of DNA for PCR- based from forensic material.

Biotechniques. 10: 506-513

Schneider, Arlequin (version 3.5.2.2): an integrated software package for population genetics data analysis.

Evol. Bioinform. Online. 1: 47-50Article InfoPublication History

Published online: November 27, 2019

Accepted: November 27, 2019

Received in revised form: November 26, 2019

Received: September 19, 2019

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