Lynch M
Department of Ecology, Ethology and Evolution, University of Illinois, Champaign 61820.
Mol Biol Evol. 1988 Sep;5(5):584-99. doi: 10.1093/oxfordjournals.molbev.a040518.
The recent discovery of hypervariable VNTR (variable number of tandem repeat) loci has led to much excitement among population biologists regarding the feasibility of deriving individual estimates of relatedness in field populations by DNA fingerprinting. It is shown that unbiased estimates of relatedness cannot be obtained at the individual level without knowledge of the allelic distributions in both the individuals of interest and the base population unless the proportion of shared marker alleles between unrelated individuals is essentially zero. Since the latter is usually on the order of 0.1-0.5 and since there are enormous practical difficulties in obtaining the former, only an approximate estimator for the relatedness can be given. The bias of this estimator is individual specific and inversely related to the number of marker loci and frequencies of marker alleles. Substantial sampling variance in estimates of relatedness arises from variation in identity by descent within and between loci and, with finite numbers of alleles, from variation in identity in state between genes that are not identical by descent. In the extreme case of 25 assayed loci, each with an effectively infinite number of alleles, the standard error of a relatedness estimate is no less than 14%, 20%, 35%, and 53% of the expectation for full sibs and second-, third-, and fourth-order relationships, respectively. Attempts to ascertain relatedness by means of DNA fingerprinting should proceed with caution.
最近对高变VNTR（可变串联重复序列）位点的发现，让群体生物学家对通过DNA指纹识别得出野外种群个体亲缘关系估计值的可行性感到十分兴奋。结果表明，除非无关个体间共享标记等位基因的比例基本为零，否则在不了解感兴趣个体和基础种群等位基因分布的情况下，无法在个体层面获得无偏的亲缘关系估计值。由于后者通常在0.1 - 0.5的范围内，且获取前者存在巨大的实际困难，所以只能给出一个近似的亲缘关系估计值。该估计值的偏差因个体而异，且与标记位点的数量和标记等位基因的频率呈反比。亲缘关系估计中的大量抽样方差源于位点内和位点间同源相同性的变异，以及在等位基因数量有限的情况下，非同源相同基因间状态相同性的变异。在检测25个位点的极端情况下，每个位点都有有效无限数量的等位基因，亲缘关系估计值的标准误差分别不低于全同胞以及二级、三级和四级关系预期值的14%、20%、35%和53%。通过DNA指纹识别确定亲缘关系的尝试应谨慎进行。
