Analysis of mutation rate of 17 y-chromosome short tandem repeats loci using Tanzanian father-son paired samples

MSc Thesis

In the present study, 100 unrelated father-son buccal swab sample pairs 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 17 Y-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 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 0.609. The results shows that fathers’ age at son’s birth may have confounding effect on Y-STRs mutation rate analysis though this age difference is statistically not significant using un paired 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 short tandem repeats 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 the minimum of two 17 Y-STRs loci.

Tanzania Government Chemist Laboratory Agency (GCLA)