Application of Microhaplotypes in Sibling Kinship Testing / 法医学杂志

OBJECTIVES@#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.@*CONCLUSIONS@#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.

Calculation of Likelihood Ratios for Incest Cases Using IBD Patterns / 法医学杂志

OBJECTIVES@#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.@*CONCLUSIONS@#The calculations of LR for incest cases were illustrated based on IBD patterns.

Evaluation of Detection Efficiency for Trio Full Sibling Testing / 法医学杂志

OBJECTIVES@#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.@*CONCLUSIONS@#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.

Equation Derivation of the Probability Distribution of IBS Score among Full Sibling Pairs / 法医学杂志

Objective To derive the general equation of the probability distribution of identity by state （IBS） score among biological full sibling pairs by calculating STR allele frequency. Methods Based on the Mendelian genetics law and the hypothesis that parents of biological full siblings （FS） were unrelated individuals, the IBS score and corresponding probability of different genotype combinations in the offspring when unrelated individuals of different genotype combinations give birth to two offsprings were derived. Results Given fi （i=1, 2, …, m） as the frequency of the ith allele of a STR locus, the probability of sharing 2 alleles （p2FS）, 1 allele （p1FS） or 0 allele （p0FS） with biological full sibling pairs on the locus can be respectively expressed as follows： (see the text). The sum of p2FS, p1FS and p0FS must be 1. As for the multiple genotyping system that contained n STR loci, IBS scores between biological full sibling pairs conform to binomial distribution： IBS~B（2n, π1）. The population rate π1, can be given by the formula： (see the text). Conclusion The alternative hypothesis in biological full sibling testing is that two appraised individuals are biological full siblings. The probability of the corresponding alternative hypothesis of any STR locus combination or IBS score can be directly calculated by the equations presented in this study, and the calculation results are the basis for explanations of the evidence.

Formula Derivation for the Probability Distribution of IBS Score in Unrelated Individual Pairs / 法医学杂志

@#Objective To derive the general equation of the probability distribution of identity by state （IBS） score among biological full sibling pairs by calculating STR allele frequency. Methods Based on the Mendelian genetics law and the hypothesis that parents of biological full siblings（FS） were unrelated individuals, the IBS score and corresponding probability of different genotype combinations in the offspring when unrelated individuals of different genotype combinations give birth to two offsprings were derived. Results Given fi （i=1, 2, …, m） as the frequency of the ith allele of a STR locus, the probability of sharing 2 alleles（p2FS）, 1 allele（p1FS） or 0 allele （p0FS） with biological full sibling pairs on the locus can be respectively expressed as follows： p2FS= 14 ×[1 + 2∑im= 1 fi2 + 2（∑im= 1 fi2）2 -∑im= 1 fi4] , p1FS= 12 ×[1 +∑im= 1 fi2 - 2（∑im= 1 fi2）2 - 2∑im= 1 fi3 + 2∑im= 1 fi4] and p0FS= 14 ×[1 - 4∑im= 1 fi2 + 2（∑im= 1 fi2）2 + 4∑im= 1 fi3 -3∑im= 1 fi4] . The sum of p2FS, p1FS and p0FS must be 1. As for the multiple genotyping system that contained n STR loci, IBS scores between biological full sibling pairs conform to binomial distribution：IBS~B（2n, π1）. The population rate π1, can be given by the formula：π1= 1n∑ln= 1 p2FSl + 21n∑ln= 1 p1FSl . Conclusion The alternative hypothesis in biological full sibling testing is that two appraised individuals are biological full siblings. The probability of the corresponding alternative hypothesis of any STR locus combination or IBS score can be directly calculated by the equations presented in this study, and the calculation results are the basis for explanations of the evidence.

Formula Derivation for the Probability Distribution of IBS Score in Unrelated Individual Pairs / 法医学杂志

OBJECTIVES@#To derive the probability equation given by STR allele frequencies of identity by state （IBS） score shared by unrelated individual pairs.@*METHODS@#By comparing the STR genotypes of two unrelated individuals, three mutually exclusive combinations could be obtained： （1） sharing 2 identical alleles, a₂=1, otherwise a₂=0; （2） sharing 1 identical allele, a₁=1, otherwise a₁=0; （3） sharing 0 identical allele, a₀=1, otherwise a₀=0. And the IBS score of the one STR locus in this unrelated individual pair could be given by the formula： ibs=2a₂+a₁. The probability of a₂=1 （p₂）, a₁=1 （p₁） and a₀=1 （p₀） were derived and expressed in powers of the allele frequencies. Subsequently, for a genotyping system including n independent STR loci, the characteristics of binomial distribution of IBS score shared by a pair of unrelated individuals could be given by p₂l and p₁l （l=1, 2, …, n）.@*RESULTS@#All the general equations of p₂, p₁ and p₀ were derived from the basic conceptions of a₂, a₁ and a₀, respectively. Given fi （i=1, 2, …, m） as the ith allele frequency of a STR locus, the general equations of p₂, p₁ and p₀ could be respectively expressed in powers of fi： [Formula: see text],[Formula: see text] and [Formula: see text]. The sum of p₂, p₁ and p₀ must be equal to 1. Then, the binomial distribution of IBS score shared by unrelated individual pairs genotyped with n independently STR loci could be written by： IBS~B（2n, π）, and the general probability, π, could be given by the formula： [Formula: see text].@*CONCLUSIONS@#In the biological full sibling identification, the probability of null hypothesis corresponding to any specific IBS score can be directly calculated by the general equations presented in this study, which is the basement of the evidence explanation.

Research siblings identification by Identiffler system and automatic STR genetic / 中国法医学杂志

Objective To evaluate the probability of siblings identification in Identifiler system by using the software of automatic analysis.Methods Using the software of automatic analysis in siblings jdentification.STP genetic typing of 151 pairs of full siblings and 31224 pairs of unrelated individuals from manual simulation were analyzed in 15 STR loci of ldentifiler system.Results Kin probability(W_(FS))of 39.07% full siblings were more than 99.999% while W_(FS) of unrelated individual pairs were 0% .W_(FS) of 60.93% full siblings and 21.3% unrelated individual pairs were all at the range from 99.999% to 1% .W_(FS) of 78.7% unrelated individual pairs 0% full siblings individuals were less than 1% .Therefore,there were notability difference between full siblings and unrelated individual pairs.In addition,testing of 15 STR loci of Identifiler system,it suggested that the pair were siblings when the locus number of the entirely-same is not less than 5 or that of the entirely-different is not more than 1,and that the pair were unrelated individuals when the locus number of the entirely-different is not less than 6 or that of the entirely-8alne is not more than 1.Conclusion The software of automatic analysis and the Identifiler system call be used to siblings identification.

Application of autosomal STR genetic markers in siblings identification / 中国法医学杂志

Objective To discuss the probability of siblings identification by autosomal short tandem repeat (STR). Methods 150 pairs of full siblings and 150 pairs of unrelated individuals were genotyped by the 15 STR loci of Power Plex?6 system. Paternity index of full siblings (Pips) and paternity probability of full siblings (WFS) were calculated with the method of ITO. WFS and allelic matching of the two groups were compared, and three sorts of allelic matching in each pair were tested by chi-square test. Results Wps of 100 pairs of siblings (66.67%) were more than 0.9995; WFS of unrelated individuals were less than 0.8, and that of 100 pairs (66.67%) were less than 0.27. The locus number of the entire-same ranged from 1 to 10, averaged 5.49 in siblings, while in unrelated individuals ranged from 0 to 5 and averaged 1.33; that of the entire-different ranged from 0 to 6, averaged 1.66 in siblings but ranged from 2 to 11 and averaged 6.57 in unrelated individuals; that of the half-same ranged from 3 to 13, averaged 7.85 in siblings, and ranged from 1 to 13, averaged 7.11 in unrelated individuals. By chi-square test, there was significant difference (P0.05) in the half-same between the two groups. Conclusion It is effective to identify siblings by Power-Plex?6 system. Testing of 15 STR loci of PowerPlex?6 system, it suggested that the pair were unrelated individuals when the locus number of the entirely-different is not less than 6 or that of the entirely-same is zero, and that the pair were siblings when the locus number of entirely-different is not more than 1 or that of the entirely-same is not less than 6.