Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA, USA.
BMC Biol. 2010 Feb 24;8:16. doi: 10.1186/1741-7007-8-16.
A selective sweep containing the insulin-like growth factor 1 (IGF1) gene is associated with size variation in domestic dogs. Intron 2 of IGF1 contains a SINE element and single nucleotide polymorphism (SNP) found in all small dog breeds that is almost entirely absent from large breeds. In this study, we surveyed a large sample of grey wolf populations to better understand the ancestral pattern of variation at IGF1 with a particular focus on the distribution of the small dog haplotype and its relationship to the origin of the dog.
We present DNA sequence data that confirms the absence of the derived small SNP allele in the intron 2 region of IGF1 in a large sample of grey wolves and further establishes the absence of a small dog associated SINE element in all wild canids and most large dog breeds. Grey wolf haplotypes from the Middle East have higher nucleotide diversity suggesting an origin there. Additionally, PCA and phylogenetic analyses suggests a closer kinship of the small domestic dog IGF1 haplotype with those from Middle Eastern grey wolves.
The absence of both the SINE element and SNP allele in grey wolves suggests that the mutation for small body size post-dates the domestication of dogs. However, because all small dogs possess these diagnostic mutations, the mutations likely arose early in the history of domestic dogs. Our results show that the small dog haplotype is closely related to those in Middle Eastern wolves and is consistent with an ancient origin of the small dog haplotype there. Thus, in concordance with past archeological studies, our molecular analysis is consistent with the early evolution of small size in dogs from the Middle East.See associated opinion by Driscoll and Macdonald: http://jbiol.com/content/9/2/10.
胰岛素样生长因子 1（IGF1）基因的选择性清除与家犬的体型变化有关。IGF1 的内含子 2 包含一个 SINE 元件和一个单核苷酸多态性（SNP），该 SNP 在所有小型犬种中都存在，但在大型犬种中几乎完全缺失。在这项研究中，我们对大量灰狼种群进行了调查，以更好地了解 IGF1 变异的祖先模式，特别关注小型犬单倍型的分布及其与犬起源的关系。
我们提供了 DNA 序列数据，证实了 IGF1 内含子 2 区域中衍生的小型 SNP 等位基因在大量灰狼样本中缺失，并进一步证明了所有野生犬科动物和大多数大型犬种中都不存在与小型犬相关的 SINE 元件。来自中东的灰狼单倍型具有更高的核苷酸多样性，表明其起源于此。此外，PCA 和系统发育分析表明，小型家养犬 IGF1 单倍型与中东灰狼的亲缘关系更为密切。
灰狼中既没有 SINE 元件也没有 SNP 等位基因，这表明小型体型的突变发生在犬类驯化之后。然而，由于所有的小型犬都具有这些诊断性突变，这些突变很可能在犬类的早期历史中就出现了。我们的研究结果表明，小型犬单倍型与中东狼的单倍型密切相关，并且与中东地区小型犬单倍型的古老起源相一致。因此，与过去的考古研究一致，我们的分子分析与狗的小型化在中东的早期进化是一致的。
