DNA identification can be used to determine a biological relationship among individuals within a family by comparing the DNA patterns of the individuals. As a part of DNA identification, a paternity test is conducted by analyzing the DNA patterns in STR (short tandem repeat) markers. STR is DNA loci composed of the repetition of 2-6 bases. The human genome may contain various numbers and types of base repetition. DNA identification through STR markers is one of the DNA test procedures with high sensitivity because of its high variation rate between loci or individuals.
The role of molecular forensic experts has been widely known since the use of DNA as examination materials. However, DNA as an examination material of molecular forensics is problematic (Butler, 2015). Several issues could complicate the work of a molecular forensic expert during the analysis of DNA samples or in determining the results of DNA examination. Forensic personal identification is often limited by the unavailability of information from parents or children that can be used as comparisons in forensic DNA examination.
The principles of forensic DNA examination are based on the comparison between alleles of the victims or perpetrators and the alleles originating from their family line (kinship analysis), such as in unborn child disputed cases, paternity disputed cases, and, even, in the identification of mass disaster victims, or war victims. In these situations, the comparison originating from close families such as younger or older siblings is required if the comparison from the parental or filial lines is not available.
An identification process using full siblings as a comparison may face the possibility of a mismatched profile of the used DNA loci. Furthermore, the diversity of ethnicities in Indonesia has created the chance of mismatches” in personal identification using siblings DNA profiling.
Materials and methods
This study was analytical observational research. The sample consisted of peripheral blood of women in their second trimester of pregnancy and their two biological children. The number of respondents was 20 families, each of which consisted of a pregnant mother with two biological children. The total number of samples was 60. The study was conducted at Human Genetic Laboratory, Institute of Tropical Diseases [ITD] of Universitas Airlangga.
Results and discussions
The unavailability of information from the parents or children that can be used as comparisons in forensic DNA examinations hinders the forensic DNA analysis (Omran, et al. 2009; O’Connor, 2011). Unlike DNA examination with parental DNA as the comparison, the use of siblings DNA in personal identification may not have 100% precision. The siblings who are used as the comparison can be born children or unborn fetuses. In pregnant women at the age of 1-2 trimesters of the pregnancy, the blood circulatory system contains cell-free fetal DNA (cff-DNA), the DNA fragments originating from the fetus penetrating the maternal circulation. These fragments can be identified through the DNA isolation method from maternal plasma samples.
In sibship/sibling analysis, allele sharing plays a significant role. The allele sharing in determining full siblings is useful in connecting the alleles when both are involved. Statistically, full siblings have the precision probability of 2 alleles as much as 25%. This probability value equals not sharing any allele or 0 (zero) shared alleles; meanwhile, the probability of 1 shared allele is 50%.
In this study, the means of allele sharing between full siblings in loci CSF1PO, THO1, TPOX, and vWA were 0 allele (13.75%), one allele (44.75%), and 2 alleles (41.50%) (shown by figure 2). The means of allele sharing found in the study was in line with the one in previous study conducted by Wenk (1996) and a theory proposed by O’ Connor (2011) showing that 1 allele sharing dominates namely 44.75%. This finding contrasts with the previous research conducted by Sosiawan (2020), revealing that 2-allele sharing was more superior. The variation was caused by the ethnicity that had a different genetic contribution among the population. The variation could be attributed to historical and demographical processes leading to genetic drift (Maeda, et al., 2005; Venkanna et al., 2008).
The result of Sibling Indices (SI) showed that 75% of pairs of full siblings, including cff-DNA, had SI more than 10 (strong and very strong) (shown by Table 3). This finding implies that the application of STR loci CSF1PO, THO1, TPOX, and vWA would be very predictive in identifying full siblings.
The findings of this study show that the mean of SI in 1 allele sharing has the highest value, as much as 44.5% in CODIS-STR loci (CSF1PO, THO1, TPOX, and Vwa). The application of cff-DNA originating from pregnant women serves as an alternative material in a paternity test, a non-invasive technique.
Authhor: Ahmad Yudianto
Detailed information from this research can be viewed in our article at :https://journals.athmsi.org/index.php/AJID/article/view/5979/3278
