Hu Yuhan, Dai Xuan, Wang Haoyu, Wei Yifan, Cai Yuntao, Yang Chun, Zhu Qiang, Zhang Ji
West China School of Basic Medical Sciences & Forensic Medicine, Sichuan University, Ren Min Nan Road 3-17, P.O.Box: 610041, Chengdu, P. R. China.
Int J Legal Med. 2025 Sep 9. doi: 10.1007/s00414-025-03572-5.
The likelihood ratio (LR) is a recommended metric for assessing the strength of genetic information in relationship testing, one of the most important tasks in forensic science. LR calculation incorporate population frequencies, which is affected by population substructure. This study utilized population frequency data from 18 short tandem repeat (STR) loci across 13 Chinese populations, encompassing both majority and minority ethnic groups. Six kinship types were constructed for each population. To understand the impact of population substructure on kinship testing, LRs were calculated using various frequency data: population-specific allele frequencies, national allele frequencies, and national allele frequencies adjusted with overall national F or population-specific F. LRs were also compared using the cutoff and comparison methods. The study found that LRs calculated using national allele frequencies tend to be the largest, which could overestimate the degree of relatedness compared to population-specific allele frequencies. Fst correction decreased the LR values, resulting in more conservative outcomes and suggested more distant relationships. While the F correction had a minimal effect on the majority and some minority populations across different kinships, it was insufficiently conservative for more isolated minority populations when the overall national F was applied. In conclusion, for isolated subpopulations with F values above the national average, utilizing population-specific allele frequencies and applying higher F values (e.g. 0.03 or 0.05) leads to more accurate and conservative inferences of relatedness. In contrast, for other groups, national frequencies without F correction appear sufficient for relationship testing.
似然比（LR）是评估亲缘关系检测中基因信息强度的推荐指标，亲缘关系检测是法医学中最重要的任务之一。LR计算纳入了群体频率，而群体频率受群体亚结构的影响。本研究利用了来自13个中国群体（包括主要民族和少数民族）的18个短串联重复序列（STR）位点的群体频率数据。为每个群体构建了六种亲属关系类型。为了解群体亚结构对亲缘关系检测的影响，使用各种频率数据计算LR：群体特异性等位基因频率、全国等位基因频率以及用全国总体F或群体特异性F调整后的全国等位基因频率。还使用截断值和比较方法对LR进行了比较。研究发现，使用全国等位基因频率计算的LR往往最大，与群体特异性等位基因频率相比，这可能会高估亲缘程度。Fst校正降低了LR值，产生了更保守的结果，并表明亲缘关系更远。虽然F校正对不同亲属关系中的大多数群体和一些少数群体影响最小，但在应用全国总体F时，对于更孤立的少数群体来说，其保守性不足。总之，对于F值高于全国平均水平的孤立亚群体，使用群体特异性等位基因频率并应用更高的F值（例如0.03或0.
