Application efficacy evaluation of the STRSeqTyper122 kit and the FASTASeq 300 second generation sequencer in kinship...

Forensic DNA technology is the method of choice for kinship identification. However, existing standard methods still have certain limitations in accurately determining the range of kinship relationships. China's independently developed second generation sequencing technology and equipment are expected to enhance the capability of forensic DNA kinship identification. In this study, we utilized the STRSeqTyper122 second generation sequencing STR typing kit and the FASTASeq 300 second generation sequencer to analyze 107 real kinship samples. The analysis included 63 autosomal STR loci, 42 Y-STR loci, 16 X-STR loci, and one gender-determining locus, Amel. The samples covered various kinship relationships, including 113 parent-child pairs, 48 full-sibling pairs, 76 uncle-nephew pairs, 66 grandparent-grandchild pairs, and 4 half-sibling pairs. Combined with simulated data, the ITO method was applied to calculate the cumulative likelihood ratio (CLR) for different levels of kinship based on the length polymorphism and sequence polymorphism of autosomal STR loci, systematically evaluating the practical application performance of this system in kinship identification. The results showed that, using log₁₀CLR values of 4 and -4 as thresholds, the system achieved 100% efficiency in identifying real parent-child and full-sibling relationships. For second degree kinship identification, the system efficiency based on simulated length polymorphism data was 55.2%, while sequence polymorphism improved it to 75.11%. For real sample data, length polymorphism based efficiency was 54.45%, and sequence polymorphism based efficiency reached 76.71%. The findings indicate that the STRSeqTyper122 kit holds significant value in first degree kinship identification. Sequence polymorphism can improve second degree kinship identification efficiency to over 75%.