Detection of sequence-tagged sites to reveal mechanisms of multi-step mutations at multi-copy Y-STRs in father-son pairs.

The case report demonstrates that co-examining various forensic markers with different technologies can strengthen the connection between father-son pairs with multi-step mutations observed at multi-copy Y-chromosomal short tandem repeats (Y-STRs). We detect 33 autosomal STRs and 94 identity-informative single nucleotide polymorphisms (iSNPs) using capillary electrophoresis (CE) and/or next-generation sequencing (NGS) to confirm the relationship within pedigrees. Meanwhile, this study reveals that the mechanisms behind the mutations observed in these cases involve STR slippage (identified using NGS or Sanger sequencing methods) and/or chromosomal structure rearrangement (identified using sequence-tagged site analyses). Such rearrangement can result in one or more step mutations. Loci within the same rearrangement region will also be linked and 'mutate' simultaneously. The chromosomal structure rearrangement rate observed in this study is calculated as 0.0012 (95% confidence interval: 0.0002-0.0034) in Northern Han Chinese.