**1. Introduction**

Brazil has several breeds of sheep, including animals that developed from breeds brought by settlers soon after the discovery. Over the years, these animals were under the process of natural selection of local environmental and climatic conditions, resulting in breeds that are considered naturalized, locally adapted or native [1].

Thus, the characterization of the diversity of naturalized breeds, the genetic relationship between them, as well as knowledge of their origins in other breeds are the first step to obtain subsidies for breeding programs, management, and conservation of naturalized Brazilian sheep [2].

Molecular tools and recent technologies have marked the discovery of the source and domes‐ tication processes of species, both using molecular markers such as mitochondrial DNA (mtDNA). These tools have aided the understanding of evolutionary relationships, taxono‐ mies, demographics of various species and provided support to identify the most important areas for conservation programs, and assist in the analysis of genetic diversity in domestic animals, wildlife, and endangered species [3, 4].

The mtDNA shows the haplotype diversity within species; therefore, it becomes a useful tool to establish phylogenetic relationships between the species [5]. On the other hand, the haploid inheritance of markers of the Y chromosome makes them to be extremely sensitive for detecting genetic history, the process of domestication, the relationship between population and the male abundance in gene flow [6].

The Pantaneiro sheep showed greater allelic richness when compared with other populations in a study with other six breeds in the state of Mato Grosso do Sul, Brazil [7]. Considering that the introduction of sheep in South America has occurred concomitant with the process of colonization and the effective population size is in process of formation, high levels of diversity observed in the different studied populations can be related to the fact of selective pressure coupled with miscegenation have implicated in the introgression of genes in populations.

Analyzing the haplotypes found in mtDNA, it was observed that the Pantaneiro sheep was distributed in seven haplotypes and grouped with all other locally adapted breeds that were analyzed [8].

A study performed with Creole breed demonstrated that these animals have a different haplotype compared to the animals of Pantaneiro breed, as there was no grouping in the same network [9]. This suggests a difference between these groups, so more research would be needed to see if it is enough that the Pantaneiro sheep can be recognized as a distinct breed [10]. However, it was also observed that several haplotypes for the Creole breed were close to haplotype formed by Pantaneiro breed which could indicate that, although these animals do not share the same haplotype, they belong to the same haplogroup. The regions where these animals currently found previously belonged to Paraguay, so it is possible that Pantaneiro breed has been influenced by Paraguayan herds. Analysis of their mitochondrial genome can redeem this history showing their genetic diversity from the Creole breed. Thus, the existence of significant differences in the ND5 gene of mtDNA between Pantaneiro and Creole breeds could indicate that differentiation has occurred between the two breeds, but further research using other markers would be needed to prove the differentiation between Pantaneiro and Creole.

Research shows the importance of exploiting the potential of the genetic diversity found in locally adapted livestock. Innate genes with adaptive values linked to tropical climatic regions compared to breeds created/improved in temperate environments could be highly useful in view of the climate changes predicted for the coming years. The exotic breeds, although considered high performance, can reduced their productivity by not easily conform to the conditions of creation and management taxes in Brazil, combined yet to climatic weather (tropical). The introgression of genes between these populations can produce animals whose general average production and rusticity exceed the means of the parents.

A few studies demonstrated that Pantaneiro breed served as maternal basis for the formation of other breeds reared in the region [8, 11]. Moreover, it is possible to suggest an European origin for the sheep populations studied; therefore, more studies using more markers are needed so that it is possible to prove their origin.

It is assumed therefore that the establishment of conservation programs using molecular tools is crucial to provide information regarding the genetic diversity patterns of locally adapted groups, and allow the same to be used for the production system, adding adaptation features, and rusticity [12].
