Abstract
ABSTRACT Background: Short Tandem Repeats (STR), which are characterized by genetic polymorphism, are powerful genetic markers widely used in forensic genetic fields. Unfortunately, mutations in different STR loci may make interpreting STR data difficult. As a result, the mutation rate of STR loci is crucial for data interpretation in human identification and paternity testing. Aim: This study aims to determine locus-specific mutations of 15 autosomal STR markers used in paternity testing in the Libyan population and calculate the mutation rate of these 15 autosomal STR markers. Materials and Method: To confirm that the STR loci have been mutated in the Libyan population, we investigated the mutation of autosomal STRs in paternity tests, including 172 trios and duos sets, in a DNA fingerprint laboratory, over a period of four years (2012-2015) by using AmpFlSTR® Identifiler™, AmpFlSTR® IdentifilerPlus™ kits from applied biosystem. We analyzed 3285 parent-child meiotic allelic transfer, including 15 autosomal STRs, that corresponded to the expanded CODIS core of 15 STRs (D8S1179, D7S820, D5S818, D3S1358, CSF1PO, THO1, FGA, D21S11, D19S433, D2S1338, VWA, TPOX, D18S51, D16S539, and D13S317). Results: We detected nine mutation events in 7/15 loci in 219 meiosis numbers. Six cases out of the nine detected allelic changes were one-step mutations, two cases were two-step mutations, and one case was a three-step mutation. The proportion of paternal versus maternal mutations was 6:3. We observed that mutations caused by the deletion of a repetitive unit occurred more frequently than mutations caused by the insertion of a unit, where the ratio between them was 5:4. D7S820, D3S1358, TH01, D13S317, D19S433, D2S1338, and VWA were all found to be mutation-free. The overall germline mutation rate across the 15 STR loci was 2.74 ×10-3. The observed mutation rates across the 15 STR loci ranged from 0.0000 to 0.00913. The highest mutation rates were observed at loci D8S1179 and D21S11, while the lowest mutation rate was observed in CSF1PO, D18S51, D16S539, FGA and TPOX. Conclusion: This work is the first attempt to generate a local database of autosomal STR mutations for the population of Libya to be used in forensic genetic analysis. The findings of this study are critical for determining the correct likelihood ratio in the Libyan population if mutation rates are to be used. Therefore, it has been determined that more research with a larger population is required for the interpretation of STR loci where no mutations have been identified