 Genetic studies to date have been inconclusive about the closest relative of the Sorraia . On one hand , studies using mitochondrial DNA showed a relationship with the Przewalski 's Horse , in that Przewalski 's Horse has a unique <unk> ( <unk> ) not found in domestic horses , which differs by just one single nucleotide from one of the major Sorraia <unk> ( <unk> , later <unk> ) . In comparison , genetic distances within the domestic horse are as large as 11 nucleotide differences . However , this relationship with the Przewalski 's Horse was contradicted in another study using <unk> data that showed that the genetic distance between the <unk> 's Horse and the Sorraia was the largest . Such conflicting results can arise when a population passes through a genetic bottleneck , and evidence suggests that the Sorraia , among other rare breeds , has recently passed through a bottleneck , effectively obscuring the position of this breed in the family tree of the domestic horse . Thus , the morphological , physiological , and cultural characteristics of the Sorraia are the subject of continued study to better understand the relationship between various Iberian horse breeds and wild horse subspecies . 
