Abstract
Hundred unrelated father-son buccal swab sample pairs collected from consented Tanzanian population were examined to establish mutation rates using 17 Y-STRs loci DYS19, DYS389I, DYS389II, DYS390, DYS391, DYS392, DYS393, DYS385a, DYS385b, DYS437, DYS438, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 of the AmpFlSTRYfiler kit used in forensics and paternity testing. Prior to 17 Y-STRs analysis, father-son pair biological relationships were confirmed using 15 autosomal STRs markers and found to be paternally related. A total of four single repeat mutational events were observed between father and sons. Two mutations resulted in the gain of a repeat and the other two resulted in a loss of a repeat in the son. All observed mutations occurred at tetranucleotide loci DYS389II, DYS385a, and DYS385b. The locus specific mutation rate varied between 0 and 1.176 x10−3 and the average mutation rate of 17Y-STRs loci in the present study was 2.353x10−3 (6.41x10−4 - 6.013x10−3) at 95% CI. Furthermore the mean fathers' age with at least one mutation at son's birth was 32 years with standard error of 2.387 while the average age of all fathers without mutation in a sampled population at son's birth was 26.781 years with standard error of 0.609. The results shows that fathers' age at son's birth may have an effect on Y-STRs mutation rate analysis, though this age difference was statistically not significant using unpaired samples t-test (p = 0.05). As a consequence of observed mutation rates in this study, the precise and reliable understanding of mutation rate at Y-chromosome STR loci is necessary for a correct evaluation and interpretation of DNA typing results in forensics and paternity testing involving males. The criterion for exclusion in paternity testing should be defined, so that an exclusion from paternity has to be based on exclusion constellations at a minimum of two 17 Y-STRs loci.
Highlights
Research and application of Y-chromosome short tandem repeats (Y-STRs) have proven beneficial in a number of fields including paternity, anthropology, and genealogical studies [1]
Among 100 father-son pairs analyzed at the same 17 Y-STRs loci, there was no observation of multiple Y-chromosome microsatellite mutation within the same germline transmission or nonuniform alleles such as microvariants, duplication, and triplication that have been previously reported by Laouina [11] in Moroccan population
The highly polymorphic Y-STR locus DYS385 was observed to have a higher mutation rate compared to all other Y-STRs loci analyzed (Table 2)
Summary
Research and application of Y-chromosome short tandem repeats (Y-STRs) have proven beneficial in a number of fields including paternity, anthropology, and genealogical studies [1]. Human Y-STR polymorphisms or microsatellites are useful in resolving and relating male lineages in forensics especially in sexual assault cases where there is a large proportion of mixed male/female stains [2], genealogical [3], evolutionary studies [4], and anthropological applications [5]. The interpretation of DNA evidence in forensic analysis and paternity testing is based on the similarities or differences at a genetic loci used. The difference at inheritable genetic marker loci between the putative father and the offspring is attributed to nonbiological paternity and leads to exclusion of biological paternity. The spontaneous mutations in the germline of the putative father at any genetic marker locus used in the analysis can lead to an erroneous exclusion because such mutation results in differences between the parent and offspring. Since new alleles occur due to the mutation events, there is natural correlation between the degree of polymorphism and the underlined mutations rate of any given locus; i.e., the higher the mutation rate is, the more variable the locus is [6]
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