shared with other predominantly dun-colored breeds, such as the Fjord horse. Purebred Sorraia occasionally have white markings, although they are rare and undesired by the breed's studbook. Genetics The relationship between the Sorraia and other breeds remains largely undetermined, as is its relationship to the wild horse subspecies, the Tarpan and the Przewalski's Horse. The Sorraia originally developed in the southern part of the Iberian peninsula. d'Andrade hypothesized that the Sorraia would be the ancestor of the Southern Iberian breeds. Morphologically, scientists place the Sorraia as closely related to the Gallego and the Asturcon, but genetic studies using mitochondrial DNA show that the Sorraia forms a cluster that is largely separated from most Iberian breeds. Some evidence links this cluster with Konik and domestic Mongolian horses. At the same time, one of the maternal lineages is shared with the Lusitano. Genetic evidence has not supported a hypothesis that the Sorraia is related to the Barb horse, an African breed introduced to Iberia by the Moors. Multiple authors have suggested that the Sorraia might be a descendant of the Tarpan based on shared morphological features, principally the typical color of its coat. Other authors simply state that the Sorraia has "evident primitive characteristics", although they do not refer to a specific ancestor. However, there have been no genetic studies comparing the Sorraia with the Tarpan, and similarity of external morphology is an unreliable measure of relatedness. 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 haplotype (A2) not found in domestic horses, which differs by just one single nucleotide from one of the major Sorraia haplotypes (JSO41, later A7). 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 microsatellite data that showed that the genetic distance between the Prewalski'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