Adeyemo Adebowale A, Chen Guanjie, Chen Yuanxiu, Rotimi Charles
College of Medicine, University of Ibadan, Ibadan, Nigeria.
BMC Genet. 2005 Jun 24;6:38. doi: 10.1186/1471-2156-6-38.
Africa contains the most genetically divergent group of continental populations and several studies have reported that African populations show a high degree of population stratification. In this regard, it is important to investigate the potential for population genetic structure or stratification in genetic epidemiology studies involving multiple African populations. The presences of genetic sub-structure, if not properly accounted for, have been reported to lead to spurious association between a putative risk allele and a disease. Within the context of the Africa America Diabetes Mellitus (AADM) Study (a genetic epidemiologic study of type 2 diabetes mellitus in West Africa), we have investigated population structure or stratification in four ethnic groups in two countries (Akan and Gaa-Adangbe from Ghana, Yoruba and Igbo from Nigeria) using data from 372 autosomal microsatellite loci typed in 493 unrelated persons (986 chromosomes).
There was no significant population genetic structure in the overall sample. The smallest probability is associated with an inferred cluster of 1 and little of the posterior probability is associated with a higher number of inferred clusters. The distribution of members of the sample to inferred clusters is consistent with this finding; roughly the same proportion of individuals from each group is assigned to each cluster with little variation between the ethnic groups. Analysis of molecular variance (AMOVA) showed that the between-population component of genetic variance is less than 0.1% in contrast to 99.91% for the within population component. Pair-wise genetic distances between the four ethnic groups were also very similar. Nonetheless, the small between-population genetic variance was sufficient to distinguish the two Ghanaian groups from the two Nigerian groups.
There was little evidence for significant population substructure in the four major West African ethnic groups represented in the AADM study sample. Ethnicity apparently did not introduce differential allele frequencies that may affect analysis and interpretation of linkage and association studies. These findings, although not entirely surprising given the geographical proximity of these groups, provide important insights into the genetic relationships between the ethnic groups studied and confirm previous results that showed close genetic relationship between most studied West African groups.
非洲拥有大陆人群中基因差异最大的群体，多项研究报告称非洲人群表现出高度的群体分层。在这方面，在涉及多个非洲群体的遗传流行病学研究中，调查群体遗传结构或分层的可能性很重要。据报道，如果没有适当考虑遗传亚结构的存在，会导致假定的风险等位基因与疾病之间出现虚假关联。在非裔美国人糖尿病（AADM）研究（西非2型糖尿病的遗传流行病学研究）的背景下，我们使用在493名无关个体（986条染色体）中分型的372个常染色体微卫星位点的数据，调查了两个国家四个族群（加纳的阿坎族和加-阿丹贝族、尼日利亚的约鲁巴族和伊博族）的群体结构或分层情况。
总体样本中没有显著的群体遗传结构。最小概率与推断的1个聚类相关，后验概率中很少有与更多推断聚类相关的情况。样本成员到推断聚类的分布与这一发现一致；每个群体大致相同比例的个体被分配到每个聚类中，族群之间差异很小。分子方差分析（AMOVA）表明，群体间遗传方差成分小于0.1%，而群体内成分则为99.91%。四个族群之间的成对遗传距离也非常相似。尽管如此，群体间较小的遗传方差足以区分两个加纳群体和两个尼日利亚群体。
在AADM研究样本所代表的四个主要西非族群中，几乎没有证据表明存在显著的群体亚结构。族群显然没有引入可能影响连锁和关联研究分析与解释的不同等位基因频率。鉴于这些群体在地理上的接近性，这些发现虽然并非完全出人意料，但为所研究族群之间的遗传关系提供了重要见解，并证实了先前的结果，即大多数研究的西非群体之间存在密切的遗传关系。
