The domestication of stallions and mares can be analyzed separately by looking at those portions of the DNA that are passed on exclusively along the maternal (mitochondrial DNA or mtDNA) or paternal line (Y-chromosome or Y-DNA). DNA studies indicate that there may have been multiple domestication events for mares, as the number of female lines required to account for the genetic diversity of the modern horse suggests a minimum of 77 different ancestral mares, divided into 17 distinct lineages. On the other hand, genetic evidence with regard to the domestication of stallions points at a single domestication event for a limited number of stallions combined with repeated restocking of wild females into the domesticated herds.