'Folded Sequence'Variation in a Y-STR Locus Revealed by Next-generation Sequencing Helped in Solving a 21-year-long Cold Case
STR genotyping based on the traditional capillary electrophoresis technology focuses on length polymorphisms of the markers.Sequence differences among STR isometric alleles,such as SNPs and InDels,cannot be reported.Next-generation sequencing can report abundant sequence polymorphism information of STRs,including the repetitive sequence and non-repetitive interval sequence information in STR repeat regions,as well as sequence information in flanking regions,supporting forensic applications.This article reported a 21-year-long indoor homicide case.Genotypes for 38 Y-STRs were obtained by the traditional Y-STR detection method.Y-STR sequence information was reported by using the STRSeqTyperY68 kit and next-generation sequencing technology.The STRSeqTyperY68 kit genotypes fifty-two single-copy Y-STR loci,six two-copy Y-STRs,one three-copy Y-STR,and one sex determinant locus in a single reaction tube using the MiSeq FGx sequencing platform.Full sequence-based genotypes of 67 Y-STR markers were determined for one evidence collected from crime scene and eight reference samples.After comparing the 67 Y-STR genotyping result of the crime scene evidence with the eight reference samples,we found that the length-based genotypes at DYS448 were 20 among for all these nine samples.Their repeat structures were also consistent,which were the combination of 11[AGAGAT]repeat units and 9[AGAGAT]repeat units with a non-repetitive sequence of 42 nucleotides(N42)in the middle.However,the difference lied in the 32nd base of the"folded sequence"N42 of DYS448:scene evidence and sample 1 were C,while the other seven reference samples were T.Based on a single base substitution in the N42'folded sequence'of the DYS448 locus,the case was directed and key technological support was provided.This article further explored sequence variations in the N42'folded sequence'of DYS448 in different populations,as well as detailed information on loci with'folded sequence'in the STRSeqTyperY68 kit,providing reference for related research and case applications.
forensic geneticsnext-generation sequencingY-STRsequence polymorphismcold case
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