de Meeûs Thierry, Humair Pierre-François, Grunau Christoph, Delaye Christelle, Renaud François
Génétique et Evolution des Maladies Infectieuses, Equipe Evolution des Systèmes Symbiotiques, UMR 2724 CNRS-IRD, BP 64501, 911 Av. Agropolis, 34394 Montpellier Cedex 5, France.
Int J Parasitol. 2004 Jul;34(8):943-50. doi: 10.1016/j.ijpara.2004.04.006.
Microsatellite loci are usually considered to be neutral co-dominant and Mendelian markers. We undertook to study the inheritance of five microsatellite loci in the European Lyme disease vector, the tick Ixodes ricinus. Only two loci appeared fully Mendelian while the three others displayed non-Mendelian patterns that highly frequent null alleles could not fully explain. At one locus, IR27, some phenomenon seems to hinder the PCR amplification of one allele, depending on its origin (maternal imprinting) and/or its size (short allele dominance). DNA methylation, which appeared to be a possible explanation of this amplification bias, was rejected by a specific test comparing the amplification efficiency that did not differ between unmethylated and experimentally methylated DNA. The role of allele size in heterozygous individuals was then revealed from the data available on field collected ticks and consistent with the results of a theoretical approach. These observations highlight the need for prudence while inferring reproductive systems (selfing rates), parentage or even allelic frequencies from microsatellite markers, in particular for parasitic organisms for which molecular approaches often represent the only way for population biology inferences.
微卫星位点通常被认为是中性共显性孟德尔标记。我们着手研究欧洲莱姆病媒介蜱（蓖麻硬蜱）中五个微卫星位点的遗传情况。只有两个位点呈现完全孟德尔遗传模式，而其他三个位点表现出非孟德尔模式，这无法完全用高频无效等位基因来解释。在一个位点IR27，某些现象似乎会阻碍一个等位基因的PCR扩增，这取决于其来源（母本印记）和/或其大小（短等位基因优势）。DNA甲基化似乎是这种扩增偏差的一个可能解释，但通过比较未甲基化和实验甲基化DNA的扩增效率的特定测试排除了这种可能性。然后，从野外采集的蜱的现有数据中揭示了等位基因大小在杂合个体中的作用，这与理论方法的结果一致。这些观察结果强调，在从微卫星标记推断生殖系统（自交率）、亲本关系甚至等位基因频率时需要谨慎，特别是对于寄生生物，分子方法往往是进行群体生物学推断的唯一途径。
