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.
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 [
The interpretation of DNA evidence in forensic analysis and paternity testing is based on the similarities or differences at a genetic loci used. In parenthood testing, the difference at inheritable genetic marker loci between the putative father and the offspring is attributed to nonbiological paternity and therefore leads to exclusion of biological paternity. On the other hand, 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 [
In forensic DNA typing applications, highly polymorphic loci are usually preferred due to their high power of discrimination. Therefore, short tandem repeat (STR) loci or microsatellites are considered to be the markers of choice in forensics because of their high power of discrimination and ease of analysis. For criminal and paternity testing investigations, which involve males with deceased alleged father, Y-STRs are used as the marker of choice [
During this study, buccal swab samples were collected from consented father-son paired samples whose biological relationship was confirmed by autosomal STRs using AmpFlSTR Identifiler kit [
Analysis of locus specific mutation characteristics using 17 Y-STRs loci in Tanzanian father-son pairs of DNA confirmed biological paternity revealed four mutations events which were identified on DYS385a, DYS385b, and DYS389II among 17Y-STRs loci analyzed [
Mutation count and Y-STRs loci mutation characteristics events as revealed by direct observation on father-son paired samples of previously confirmed biological relationship.
Sample ID’s | Loci | Repeat |
Father’s profile | Son’s |
Mutation |
Mutation count |
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F/C003 | DYS385b | GAAA | 16 | 17 | Gain | 1 |
F/C012 | DYS385a | AAGG | 15 | 16 | Gain | 1 |
F/C074 | DYS385a | AAGG | 16 | 15 | Loss | 1 |
F/C082 | DYS389II | CTGT/CTAT | 31 | 30 | Loss | 1 |
However, no mutation event was observed for DYS19, DYS389I, DYS390, DYS391, DYS392, DYS393, DYS437, DYS348, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 loci analyzed. The observed locus specific mutation rate ranged between 0 for DYS19, DYS389I, DYS390, DYS391, DYS392, DYS393, DYS437, DYS348, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 loci and 1.765 × 10−3 (1.43x10−4– 4.243x10−3) for DYS385a locus at 95% CI [
The highly polymorphic Y-STR locus DYS385 was observed to have a higher mutation rate compared to all other Y-STRs loci analyzed (Table
Mutation count, mutation rate and 95% confidence interval (CI) for the 17 Y-STRs loci studied using Tanzanian father-son paired samples.
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DYS19 | CTAT/CTAC | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS389I | AAGG/GAAA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS389II | CTGT/CTAT | 1 | 1700 | 5.88x10−4 | 1.5x10−5 – 3.273x10−3 |
DYS390 | CTGT/CTAT | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS391 | CTGT/CTAT | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS392 | ATT | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS393 | GATA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS385a | AAGG | 2 | 1700 | 1.176x10−3 | 1.43x10−4– 4.243x10−3 |
DYS385b | GAAA | 1 | 1700 | 5.88x10−4 | 1.5x10−5 – 3.273x10−3 |
DYS438 | TTTTC/TTTTA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS439 | GATA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS437 | TCTA/TCTG | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS448 | AGAGAT | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS458 | GAAA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS456 | AGAT | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
DYS635 | TCTA/TGTA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
Y GATA H4 | TAGA | 0 | 1700 | 0.000 | 0.000 – 2.168x10−3 |
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All observed mutation events were characterised by single-step mutations (Table
In addition, two tetranucleotide microsatellites loci DYS385 and 389II appeared to consist of higher average mutation rates among all 17 Y-STRs analyzed compared to all other trinucleotide and dinucleotide microsatellite loci [
Using 100 Tanzanian father-son paired samples with confirmed paternity covering 1700 meioses were used to estimate 17Y-STRs locus specific mutation rate. The observed average estimates of 17 Y-STRs locus specific mutation rate ranged from 0 to 1.765 × 10−3 (1.43x10−4 - 4.243x10−3) at 95% CI. The higher average locus specific mutation rate was found at DYS385a locus while mutation rates of 5.88x10−4 (1.5x10−5 – 3.273x10−3) at 95% CI were observed for both DYS385b and DYS389II loci. There was no mutation observed for DYS19, DYS389I, DYS390, DYS391, DYS392, DYS393, DYS437, DYS348, DYS439, DYS448, DYS456, DYS458, DYS635, and Y-GATA-H4 loci analyzed [
The average mutation rate across all markers in this study was 2.353x10−3(6.41 × 10−4 - 6.013x10−3) at 95% CI [
The average mutation rate for 17Y-STRs loci found in this research study is greater than those calculated by Viera-Silva [
The results of present study are in general agreement with the fore mentioned research findings in which all the same 17 Y-STRs set or other number Y-STRs loci used the average mutation rate observed were in the order of 10−3 though number of father-son pairs varied between the mentioned studies above. Since there were no significant differences in mutation rate observed, therefore the mutation rates analysis does not depend on the sample size or number of Y-STRs loci used but population diversity [
The present study shows that the average 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 (Table
Fathers’s age at the time of Sons’ birth with at least one mutation and without any mutation on 17 Y-STRs loci.
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25,40,32,31 | 19,20,26,25,30,21,25,26,24,30,32,30,21,28,30,30,24,25,34,20 |
35,18,19,18,19,20,32,36,32,33,34,32,21,20,25,34,29,28,35,25 | |
24,26,25,24,26,25,34,23,25,24,28,29,25,26,23,24,27,28,36,26 | |
37,25,34,20,34,18,19,18,19,39,32,33,32,33,36,32,42,34,20,18 | |
18,19,26,19,20,32,33,32,33,36,25,20,24,18,29,19 | |
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The results of 17-Y-STRs mutation observed from this study revealed that the precise and reliable understanding of mutation rate at Y-chromosome short tandem repeats loci is necessary for a correct evaluation and interpretation of DNA typing results in forensics and paternity testing involving males. Based on the findings, the criterion for exclusion in paternity testing should be defined in any DNA testing laboratory using 17-Yfiler Amplification kits, so that an exclusion from paternity has to be based on exclusion constellations at the minimum of two 17 Y-STRs loci.
The mutation data used to support the findings of this study are included within the articles. The generated Sons’ Y-STRs haplotype data were only submitted to YHRD (http://www.yhrd.org/) and received the Accession no. YC000312.
The study and permission to publish have been approved by Medical Research Coordinating Committee (MRCC) of National Institute for Medical Research (NIMR), Tanzania. Permit nos. NIMR/HQ/R.8a/VOL.IX/1826 and NIMR/HQ/P.12 VOLXIX/34 were obtained.
Informed consent was obtained from all individual participants included in the study.
The analyses were carried out at forensic biology and DNA laboratory, Government Chemist Laboratory Authority.
The authors declare that they have no conflicts of interest.
This study was funded by the Government Chemist Laboratory Authority (GCLA). Fidelis Charles Bugoye is a recipient of a scholarship from GCLA through technical capacity training program.