Adams Susan M, King Turi E, Bosch Elena, Jobling Mark A
Department of Genetics, University of Leicester, University Road, Leicester LE1 7RH, UK.
Forensic Sci Int. 2006 May 25;159(1):14-20. doi: 10.1016/j.forsciint.2005.06.003. Epub 2005 Jul 18.
The Y-chromosomal binary marker P25 is a paralogous sequence variant, rather than a SNP: three copies of the P25 sequence lie within the giant palindromic repeats on Yq, and one copy has undergone a C to A transversion to define haplogroup R1b (designated C/C/A). Since gene conversion is known to be active in the palindromic repeats, we reasoned that P25 might be liable to back-mutation by gene conversion, yielding the ancestral state C/C/C. Through analysis of a set of binary markers in Y-chromosomes in two large samples from Great Britain and the Iberian Peninsula we show that such conversion events have occurred at least twice, and provide preliminary evidence that the reverse conversion event (yielding C/A/A) has also occurred. Because of its inherent instability, we suggest that P25 be used with caution in forensic studies, and perhaps replaced with the more reliable binary marker M269.
Y染色体二元标记P25是一个旁系同源序列变体，而非单核苷酸多态性：P25序列的三个拷贝位于Yq上的巨大回文重复序列内，且有一个拷贝发生了从C到A的颠换，从而定义了单倍群R1b（指定为C/C/A）。由于已知基因转换在回文重复序列中活跃，我们推测P25可能易于通过基因转换发生回复突变，产生祖先状态C/C/C。通过分析来自英国和伊比利亚半岛的两个大样本中Y染色体上的一组二元标记，我们表明此类转换事件至少发生了两次，并提供了反向转换事件（产生C/A/A）也已发生的初步证据。由于其固有的不稳定性，我们建议在法医研究中谨慎使用P25，或许可用更可靠的二元标记M269取而代之。
