Limagrain Genetics, 4805 W. Old Church Road, 61821, Champaign, IL, USA.
Theor Appl Genet. 1993 Feb;85(8):1055-62. doi: 10.1007/BF00215047.
The coefficient of coancestry (fAB) between individuals A and B is the classical measure of genetic relationship. fAB is determined from pedigree records and is the probability that random alleles at the same locus in A and B are copies of the same ancestral allele or identical by descent (ibd). Recently, the proportion of molecular marker variants shared between A and B (SAB) has been used to measure genetic relationship. But SAB is an upwardly-biased estimator of fAB, especially between distantly-related lines. fAB, SAB, and adjusted (to remove bias) estimates of molecular marker similarity (f AB (M) ) were compared. RFLP banding patterns at 46 probe-restriction enzyme combinations were obtained for 23 maize inbred lines derived from the Iowa Stiff Stalk Synthetic (BSSS) maize (Zea mays L.) population, and for 4 non-BSSS lines. f AB (M) was estimated as [Formula: see text], where δ A (or δ B) was the average proportion of RFLP variants shared between inbred A (or inbred B) and the non-BSSS lines. The average fAB among 253 pairwise combinations of BSSS lines was 0.212, whereas the average SAB was 0.397. The average f AB (M) was 0.162, indicating that the upward bias in SAB was effectively removed. SAB and fAB were significantly different (α = 0.05) in 76.3% of the comparisons, whereas 24.9% of the f AB (M) values differed significantly from fAB. The latter result suggests that selection and/or drift were present during inbred line development and that fAB may not be an accurate measure of the true proportion of ibd alleles between two lines. Cluster analyses based on S AB (M) and f AB (M) grouped lines according to pedigree, although several exceptions were noted. The presence of shared molecular marker variants between unrelated lines must be considered when setting SAB-based minimum distances for varietal protection. Under simplified conditions, more than 250 molecular marker loci are necessary to obtain sufficiently precise estimates of coefficient of coancestry using molecular markers.
个体 A 和 B 之间的亲缘系数（fAB）是遗传关系的经典度量。fAB 是根据系谱记录确定的，是 A 和 B 中同一基因座上随机等位基因是同一祖先等位基因的复制品或通过血统（ibd）相同的概率。最近，A 和 B 之间共享的分子标记变异体的比例（SAB）已被用于衡量遗传关系。但是，SAB 是 fAB 的向上偏差估计值，特别是在亲缘关系较远的品系之间。比较了亲缘系数（fAB）、SAB 和分子标记相似性的调整（去除偏差）估计值（fAB（M））。从爱荷华硬秆合成群体（BSSS）玉米（Zea mays L.）中获得了 23 个玉米自交系和 4 个非 BSSS 系的 46 个探针-限制酶组合的 RFLP 带型。fAB（M）估计为[公式：见文本]，其中δ A（或δ B）是自交系 A（或自交系 B）与非 BSSS 系之间共享的 RFLP 变异体的平均比例。253 个 BSSS 系的 253 个成对组合的平均 fAB 为 0.212，而平均 SAB 为 0.397。平均 fAB（M）为 0.162，表明 SAB 的向上偏差有效去除。在 76.3%的比较中，SAB 和 fAB 显著不同（α=0.05），而 24.9%的 fAB（M）值与 fAB 显著不同。后一种结果表明，在自交系发育过程中存在选择和/或漂移，并且 fAB 可能不是两条线之间真正的血统等位基因比例的准确度量。基于 SAB（M）和 fAB（M）的聚类分析根据系谱对系进行分组，尽管注意到了一些例外。在为品种保护设置基于 SAB 的最小距离时，必须考虑无关系之间共享的分子标记变异体。在简化条件下，需要超过 250 个分子标记位点才能使用分子标记获得足够精确的亲缘系数估计值。
