Y-STR单倍型匹配概率与基因座数量关系的构建

Construct a quantity relation between matching probability of Y-STR haploid and numbers of loci

目的本文探索一种衡量Y-STR系统效能的方法,应用种群结构参数θ构建Y-STR单倍型匹配概率与基因座数量关系模型,旨在分析影响Y-STR检测系统效能进入平台期的因素,确定进入平台期的基因座数量区间。方法预测了体系中每个数量基因座对应的所有可能基因座组合子集,统计每个子集对应的θ值。统计了DNATyper Y36(36)、Y filer plus(27)、PPY23(23)、Yfiler(17)等4个常用Y-STR检测系统在3个不同数量级模型库(873、9577和83 999条)的θ值,构建数量关系模型。此外,还统计了5个Y-STR案件样本在数据库中的检索结果以验证理论模型的推导结果。结果在θ最大值的拟合曲线中,DNATyper Y36系统在3个数量级数据库中进入平台期的节点分别是27、37和55个基因座;在θ最小值的拟合曲线中,该值分别是19、25和28个基因座。结论对数据库模型的研究表明,系统中Y-STR基因座数目的增加与θ值呈反比,随着基因座数目增加,其对θ值减小的影响逐渐降低,最终会进入"停滞效应",又称"平台期"。数据库容量决定了系统进入平台期的节点,数据库容量越大,则进入平台期的节点越靠后,体系中纳入GD值较高的Y-STR基因座及快速突变基因座可促使更快进入平台期。

Objective The problem that how to assess the relationship between the number of tested loci and the matching probability(MP) of database needs to be solved. This study aims to explore a scientific method to measure the efficiency of Y-STR system, by constructing a quantity relation model between MP of Y-STR haplotypes and loci number using the population structure parameter θ, and to analyze the factors which could affect the system efficiency and the range of loci numbers when reaching the plateau. Methods All possible loci combination subsets corresponding to each number of loci in the system were predicted, and their θ values were estimated. The θ values of four commonly used Y-STR systems including DNATyperY36(36), Y Filer Plus(27), PPY23(23), and Yfiler(17) in three different magnitude database models(873, 9577, and 83999) were also analyzed to constructed the quantity relation model. Additionally, this work also made statistics of the familial search results of 5 Y-STR case samples in the practical database to verify the theory model. Results In the DNATyperY36 system, the loci numbers when reaching the plateau phase in three database models were 27, 37, and 55 respectively according to the fitting curve generated by the maximum θ values, and were 19, 25 and 28 respectively according to the fitting curve generated by the minimum θ values. Conclusion The study on the population databases indicates that the θvalue was inversely correlated with the number of Y-STR loci tested. As the number of Y-STR loci in the system increases, the effect of loci number on reduction of θ valuer decreases, and the discriminating power of the system could gradually reach a plateau. The database capacity determines the position of the system plateau. The increase of database content would postpone the plateau. In addition, the involvement of Y-STR loci with high GD value and RM Y-STR in the system can promote the plateau appeared.