Application of ITO Method in Determination of Special Half-Sibling Relationship

doi:10.12116/j.issn.1004-5619.2020.500712

Abstract

Abstract: Objective

To identify whether the relationship between Zhang A, Zhang B, Zhang C and Zhang X is the half-sibling relationship whose mother is sister （hereinafter referred to as the special half-sibling relationship） or the common first cousin relationship and discuss the application of ITO method in discriminating the special kinship.

Methods

DNA was extracted from blood stain of four identified individuals, PowerPlex^? 21 System and AGCU 21+1 STR kit were used to detect autosomal STR genetic markers. Investigator^? Argus X-12 QS kit was used to detect the X chromosome STR genetic markers, the special half-sibling index （SHSI） and first cousin index （FCI） and their likelihood ratio （LR） were calculated by ITO method.

Results

The LR results of SHSI to FCI, which were calculated based on autosomal STR genotyping and the analysis of X-STR genotyping results suggested that the relationship between Zhang A, Zhang B, Zhang C and Zhang X was inclined to be a special half-sibling relationship.

Conclusion

For the identification of special kinship, it is necessary to comprehensively apply various genetic markers according to the case. After the conclusion that shared alleles cannot be excluded from the analysis, ITO method can be further used to establish discriminant assumptions according to the specific case to obtain objective and reliable identification opinions.

Key words: forensic genetics, ITO method, short tandem repeat （STR）, sibling relationship, likelihood ratio, half-sibling index, first cousin index

CLC Number:

DF795.2

Cheng-chen SHAO, Yi-ning YAO, Yue-qin ZHOU, Zhi-ping LIU, Hong-mei XU, Jian-hui XIE, Kuan SUN. Application of ITO Method in Determination of Special Half-Sibling Relationship[J]. Journal of Forensic Medicine, 2021, 37(6): 836-840.

Figures/Tables 5

Fig. 1 Genogram in case of Zhang X having the samefather with Zhang A， Zhang B and Zhang C

Fig. 2 Genogram in case of Zhang X having a differentfather with Zhang A， Zhang B and Zhang C

Tab. 1 The likelihood ratios about two competinghypotheses Hp：（A，B）~（k0，2k1，k2） versus Hd：（A，B）~（1，0，0）

甲的基因型	乙的基因型	似然比
PP	PP	$k 0$ + $2 k 1$ / $p$ + $k 2$ / $p 2$
PP	PQ	$k 0$ + $k 1$ / $p$
PP	QQ	$k 0$
PP	QR	$k 0$
PQ	PQ	$k 0$ + $k 1$ （ $p$ + $q$ ）/（ $2 p q$ ）+ $k 2$ /（ $2 p q$ ）
PQ	PR	$k 0$ + $k 1$ /（ $2 p$ ）
PQ	RS	$k 0$

Tab. 1 The likelihood ratios about two competinghypotheses Hp：（A，B）~（k0，2k1，k2） versus Hd：（A，B）~（1，0，0）

甲的基因型	乙的基因型	似然比
PP	PP	$k 0$ + $2 k 1$ / $p$ + $k 2$ / $p 2$
PP	PQ	$k 0$ + $k 1$ / $p$
PP	QQ	$k 0$
PP	QR	$k 0$
PQ	PQ	$k 0$ + $k 1$ （ $p$ + $q$ ）/（ $2 p q$ ）+ $k 2$ /（ $2 p q$ ）
PQ	PR	$k 0$ + $k 1$ /（ $2 p$ ）
PQ	RS	$k 0$

Fig. 3 Genogram in case of C1’s mother and C2’s mother are full sibling sisters

Tab. 2 Zhang A and Zhang X’s genotyping and values of SHSI， FCI and LR on some loci for example

基因座	张X 基因型	张A 基因型	SHSI计算公式	FCI计算公式	SHSI	FCI	似然比
CSF1PO	11，12	11，12	3/8+1/4×（p₁₁+p₁₂）/（2×p₁₁×p₁₂）+ 1/8/（2×p₁₁×p₁₂）	3/4+1/8×（p₁₁+p₁₂）/（2×p₁₁×p₁₂）	2.474 0	1.266 3	1.953 7
D12S391	18，21	18，20	3/8+1/4/（2×p₁₈）	3/4+1/8/（2×p₁₈）	0.943 4	1.034 2	0.912 2
D21S11	30，30	29，30	3/8+1/4/p₃₀	3/4+1/8/p₃₀	1.277 9	1.201 4	1.063 7
TH01	9	6，8	3/8	3/4	0.375 0	0.750 0	0.500 0
vWA	14，16	14，18	3/8+1/4/（2×p₁₄）	3/4+1/8/（2×p₁₄）	0.876 0	1.000 5	0.875 6
D22S1045	11，16	11	3/8+1/4/p₁₁	3/4+1/8/p₁₁	1.491 0	1.308 0	1.140 0

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