Journal of Forensic Medicine

Methods and Research Hotspots of Forensic Kinship Testing

Ran LI, Hong-yu SUN

2023, 39(3): 231-239. DOI: 10.12116/j.issn.1004-5619.2023.530208

Abstract ( 444 )

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Kinship testing is widely needed in forensic science practice. This paper reviews the definitions of common concepts, and summarizes the basic principles, advantages and disadvantages, and application scope of kinship analysis methods, including identity by state （IBS） method， likelihood ratio （LR） method， method of moment （MoM）， and identity by descent （IBD） segment method. This paper also discusses the research hotspots of challenging kinship testing, complex kinship testing, forensic genetic genealogy analysis, and non-human biological samples.

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Research Progresses of Tri-Allelic Patterns in Autosomal STR in Forensic DNA Analysis

Xiao-yan MA, Hong-yu SUN, Qing LI

2023, 39(3): 240-246. DOI: 10.12116/j.issn.1004-5619.2023.530210

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Tri-allelic pattern in autosomal STR is a common abnormal typing phenomenon in forensic DNA analysis, which brings difficulties and uncertainties to the evaluation of the evidence weight in actual cases. This paper reviews the types, formation mechanism, occurrence frequency, genetic pattern and quantitative evaluation of evidence of the tri-allelic pattern in autosomal STR in forensic DNA analysis. This paper mainly explains the formation mechanism and genetic patterns based on different types of tri-allelic pattern. This paper also discusses the determination of tri-allelic pattern and the quantitative method of evidence evaluation in paternity testing and individual identification. This paper aims to provide references for scientific and standardized analysis of this abnormal typing phenomenon in forensic DNA analysis.

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Evaluation of Detection Efficiency for Trio Full Sibling Testing

Hui CHEN, Ran LI, Yu ZANG, Jing-yi YANG, Ri-ga WU, Hong-yu SUN

2023, 39(3): 247-253. DOI: 10.12116/j.issn.1004-5619.2023.530203

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Objective To study the detection efficiency of trio full sibling with another known full sibling reference added under different number of autosomal STR typing systems. Methods Based on 43 detection systems consisting of 13 to 55 representative autosomal STR loci，10 000 true families （full sibling group） and 10 000 false families （unrelated individual group） were randomly simulated. The full sibling index （FSI） was calculated based on the method of family reconstruction. The cumulative sibling relationship index （CFSI） of 0.000 1 and 10 000 were used as the evaluation thresholds, and the detection efficiency parameters were calculated and compared with the identification of the duo full sibling testing. Results With the increasing number of STR loci， the error rate and inability of judgement rate gradually decreased; the sensitivity， specificity, correct rate of judgment and other parameters gradually increased, and the system efficiency gradually improved. Under the same detection system， trio full sibling testing showed higher sensitivity， specificity， system efficiency and lower inability of judgement rate compared with duo full sibling testing. When the system efficiency was higher than 0.85 and inability of judgement rate was less than 0.01%， at least 20 STRs should be detected for trio full sibling testing， which was less than 29 STRs required by duo full sibling testing. Conclusion The detection efficiency of trio full sibling testing is superior to that of duo full sibling testing with the same detection system， which is an effective identification scheme for laboratories with inadequate detection systems or for materials with limited conditions.

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Analysis of Trio Half Sibling Testing

Hai-xia LI, Hui CHEN, Ran LI, Yu ZANG, Hong-yu SUN

2023, 39(3): 254-261. DOI: 10.12116/j.issn.1004-5619.2021.511202

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Objective To establish an analytical method for half sibling testing involving common three relatives’ participation. Methods Based on the half sibling testing scenarios with the known biological mother, grandfather or uncle, and two unidentified controversial half siblings participating， two opposing hypotheses were set. Lineage reconstruction according to Mendel’s law of heredity was carried out, and the calculation formula of the half sibling kinship index was derived. Verification of actual cases was carried out and the results were compared with duo half sibling testing. Results In the scenarios of the known biological mother， grandfather and uncle participating in half sibling testing, the kinship calculation formulae of 54， 91 and 99 genotype combinations for kinship index calculation were deduced respectively. The actual cases showed higher kinship indexes in trio half sibling testing compared with duo half sibling testing. Conclusion It is beneficial to obtain more genetic information for family reconstruction and improvement of the strength of genetic evidence for half sibling testing by adding known relatives.

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Identification Strategy of Biological Half Sibling Relationship

Zheng TAN, Guan-ju MA, Li-hong FU, Xiao-jing ZHANG, Qian WANG, Guang-ping FU, Qing-qing DU, Shu-jin LI

2023, 39(3): 262-270. DOI: 10.12116/j.issn.1004-5619.2023.530107

Abstract ( 507 )

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Objective To compare the application value of the likelihood ratio （LR） method and identity by state （IBS） method in the identification involving half sibling relationships， and to provide a reference for the setting of relevant standards for identification of half sibling relationship. Methods （1） Based on the same genetic marker combinations， the reliability of computer simulation method was verified by comparing the distributions of cumulated identity by state score （CIBS） and combined full sibling index in actual cases with the distributions in simulated cases. （2） In different numbers of three genetic marker combinations, the simulation of full sibling, half sibling and unrelated individual pairs, each 1 million pairs, was obtained; the CIBS, as well as the corresponding types of cumulative LR parameters， were calculated. （3） The application value of LR method was compared with that of IBS method， by comparing the best system efficiency provided by LR method and IBS method when genetic markers in different amounts and of different types and accuracy were applied to distinguish the above three relational individual pairs. （4） According to the existing simulation data， the minimum number of genetic markers required to distinguish half siblings from the other two relationships using different types of genetic markers was estimated by curve fitting. Results （1） After the rank sum test， under the premise that the real relationship and the genetic marker combination tested were the same， there was no significant difference between the simulation method and the results obtained in the actual case. （2） In most cases， under the same conditions， the system effectiveness obtained by LR method was greater than that by IBS method. （3） According to the existing data， the number of genetic markers required for full-half siblings and half sibling identification could be obtained by curve fitting when the system effectiveness reached 0.95 or 0.99. Conclusion When distinguishing half sibling from full sibling pairs or unrelated pairs， it is recommended to give preference to the LR method， and estimate the required number of markers according to the identification types and the population data， to ensure the identification effect.

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Calculation of the Paternity Index for the Alleged Father Related to the Child’s Mother

Yu-ting WANG, Qiang ZHU, Yu-han HU, Yi-fan WEI, Ting-yun HOU, Ji ZHANG

2023, 39(3): 271-275. DOI: 10.12116/j.issn.1004-5619.2023.530209

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Objective To derive the paternity index （PI） calculation formula of the alleged father （AF） when the AF is a relative （parent/child， siblings， grandparent/grandchild， uncle/nephew， first cousins） of the child’s biological mother. Methods For the case when the AF is related to the child’s biological mother， the existence of the relationship in the numerator and denominator hypothesis of PI was considered. The genotype frequency of the AF was calculated by using the frequency formula in which the mother’s genotype was considered， while the random male in the denominator was substituted as another relative of the mother’s same rank. The PI calculation formula was derived to eliminate the effect of the relationship between AF and the child’s biological mother. Results When the AF and the biological mother have first， second and tertiary kinship， a more conservative PI was obtained from the PI calculation formula derived in this study compared with the PI calculation method which did not consider kinship. Conclusion The calculation method provided in this study can eliminate the effect of the relation of the AF and mother on the PI in incest cases， to obtain more accurate and conservative identification conclusions.

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General Formulas for Calculating Commonly Used Kinship Index

Chao XIAO, Dai-xin HUANG

2023, 39(3): 276-282. DOI: 10.12116/j.issn.1004-5619.2023.530104

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Objective To derive general formulas for calculating commonly used kinship index （KI）. Methods By introducing the Kronecker symbol， the formulas used to calculate the same KI under different genotype combinations were summarized into a unified expression. Results The general formulas were successfully derived for KI in various case situations， including the paternity index， full sibling index， half sibling index， avuncular index， grandpaternity index， first-cousin index， and second-cousin index between two individuals without or with the mother being involved; grandpaternity index between grandparents and a grandchild without or with the mother being involved; half sibling index between two children with two mothers being involved; full sibling index among three children; and half sibling index among three children with no， one， or two mothers being involved. Conclusion The general formulas given in this study simplify the calculation of KIs and facilitate fast and accurate calculation through programming.

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Calculation of Likelihood Ratios for Incest Cases Using IBD Patterns

De-jian LÜ

2023, 39(3): 283-287. DOI: 10.12116/j.issn.1004-5619.2023.530109

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Objective To calculate the likelihood ratios of incest cases using identity by descent （IBD） patterns. Methods The unique IBD pattern was formed by denoting the alleles from the members in a pedigree with a same digital. The probability of each IBD pattern was obtained by multiplying the prior probability by the frequency of non-IBD alleles. The pedigree likelihoods of incest cases under different hypotheses were obtained by summing all IBD pattern probabilities, and the likelihood ratio（LR） was calculated by comparing the likelihoods of different pedigrees. Results The IBD patterns and the formulae of calculating LR for father-daughter incest and brother-sister incest were obtained. Conclusion The calculations of LR for incest cases were illustrated based on IBD patterns.

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Application of Microhaplotypes in Sibling Kinship Testing

Xuan TANG, Dan WEN, Chu-dong WANG, Ru-yi XU, Hong-tao JIA, Jie-nan LI, Bai-yi-la ZHALAGA

2023, 39(3): 288-295. DOI: 10.12116/j.issn.1004-5619.2023.530101

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Objective To investigate the efficacy of different numbers of microhaplotype (MH) loci and the introduction of different reference samples on the identification of full sibling, half sibling and differentiation between full sibling and half sibling kinships, and to explore the effect of changing mutation rate on sibling testing. Methods First, a family map involving three generations was established, and four full sibling identification models, five half sibling identification models and five models distinguishing full and half siblings were constructed for different reference samples introduced. Based on the results of the previous study, two sets of nonbinary SNP-MH containing 34 and 54 loci were selected. Based on the above MH loci, 100 000 pairs of full sibling vs. unrelated individuals, 100 000 pairs of half sibling vs. unrelated individuals and 100 000 pairs of full sibling vs. half sibling were simulated based on the corresponding sibling kinship testing models, and the efficacy of each sibling kinship testing model was analyzed by the likelihood ratio algorithm under different thresholds. The mutant rate of 54 MH loci was changed to analyze the effect of mutation rate on sibling identification. Results In the same relationship testing model, the systematic efficacy of sibling testing was positively correlated with the number of MH loci detected. With the same number of MH loci, the efficacy of full sibling testing was better than that of uncle or grandfather when the reference sample introduced was a full sibling of A, but there was no significant difference in the identification efficacy of the four reference samples introduced for full sibling and half sibling differentiation testing. In addition, the mutation rate had a slight effect on the efficacy of sibling kinship testing. Conclusion Increasing the number of MH loci and introducing reference samples of known relatives can increase the efficacy of full sibling testing, half sibling testing, and differentiation between full and half sibling kinships. The level of mutation rate in sibling testing by likelihood ratio method has a slight but insignificant effect on the efficacy.

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Application of Familial Y-STR Haplotype Mismatch Tolerance in Genealogy Inference

Meng-jie TONG, Ke ZHANG, Cai-xia LI, Guang-feng ZHANG, Wen-jie ZHANG, Lan YANG, Qing-tang HOU, Jing LIU

2023, 39(3): 296-304. DOI: 10.12116/j.issn.1004-5619.2022.520602

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Objective To provide a guideline for genealogy inference and family lineage investigation through a study of the mismatch tolerance distribution of Y-STR loci in Chinese Han male lineage. Methods Three Han lineages with clear genetic relationships were selected. YFiler Platinum PCR amplification Kit was used to obtain the typing data of 35 Y-STR loci in male samples. The variation of Y-STR haplotypes in generation inheritance and the mismatch tolerance at 1-7 kinship levels were statistically analyzed. Results Mutations in Y-STR were family-specific with different mutation loci and numbers of mutation in different lineages. Among all the mutations, 66.03% were observed on rapidly and fast mutating loci. At 1-7 kinship levels, the number of mismatch tolerance ranged from 0 to 5 on all 35 Y-STR loci, with a maximum step size of 6. On medium and slow mutant loci, the number of mismatch tolerance ranged from 0 to 2, with a maximum step size of 3; on rapidly and fast mutant loci, the number of mismatch tolerance ranged from 0 to 3, with a maximum step size of 6. Conclusion Combined use of SNP genealogy inference and Y-STR lineage investigation, both 0 and multiple mismatch tolerance need to be considered. Family lineage with 0-3 mismatch tolerance on all 35 Y-STR loci and 0-1 mismatch tolerance on medium and slow loci can be prioritized for screening. When the number of mismatch tolerance is eligible, family lineages with long steps should be carefully excluded. Meanwhile, adding fast mutant loci should also be handled with caution.

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