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Complex kinship identification such as half-sibling identification is a difficult task in forensic biology Here we represented an approach in dealing with half-sisters from different mothers, with the combination of autosomal and X chromosomal short-tandem repeats (STRs) data. X chromosomal STRs can offer additional information, especially in some cases where autosomal STRs alone may not provide enough information for an accurate opinion. In this case, half-sister or unrelated relationship between two women (S1 and S2) with different mothers were distinguished. 23 autosomal and 31 X chromosomal STRs of S1, S2, S1's mother (M1), S2's mother (M2) and S1's grandmother (G1) were profiled with three different commercial kits. As to X-chromosome STRs, likelihood ratios (LRs) were calculated by FamLinkX with consideration of linkage, linkage disequilibrium, and mutations. When only the profiles of the two individuals (S1 and S2) were available, LRs between S1 and S2 were 1.1110 × 102 based on 23 autosomal STRs and 3.2257 om107 based on 31 X chromosomal STRs. When the maternal genotypes were taken into consideration, LRs increased to 2.5297 × 103 and 3.0563 × 1018. Therefore, both the DNA profiles of each mothers and X chromosomal STRs are important in dealing with the identification of half-sisters from different mothers.

This study aimed to investigate the application of autosomal short tandem repeat (STR) loci using the ITO method and discriminant function algorithm for full-sibling (FS) identification. A total of 342 pairs of full siblings (FSs) and 3900 pairs of unrelated individuals (UIs) were genotyped at 51 STR loci. The groups were in accordance with discrimination power (DP) values and the number of loci, and the values of FS index (FSI) of FSs and UIs were calculated by the ITO method. The discriminant functions of FS–UI were established using the Fisher's discriminant analysis method with SPSS 19.0 software. All the lgFSI values in the FS and UI groups followed a normal distribution, and there were significant differences between the two pairs. A higher average DP value was associated with a more significant difference, as was a greater number of STR loci detected. Receiver operator characteristic curves showed that the accuracy of FS identification can be affected by both locus polymorphism and the number of loci detected. Comparing the rate of false positives and false negatives of discriminant function between the two groups, a higher average DP value and larger number of loci detected were associated with a lower rate of miscarriage of justice and were more helpful for FS–UI identification. The ITO-based discriminant analysis method has high applicability in FS–UI tests. Testing of a greater number of STR loci promotes FS identification.