Regarding fertility of hinnies and mules:
http://www.ncbi.nlm.nih.gov/sites/entrez...p;dopt=AbstractSeems in China both have been shown to be fertile. Could be suspect of course. And regarding Mongolian and domestic horse hybrids:
http://www.iht.com/articles/2005/10/12/healthscience/snhorses.phpFrom the article:
"Teri Lear, an expert in horse genetics at the University of Kentucky, said comparisons of mitochondrial DNA, the genetic material inherited through the maternal line, showed that the P-horse and the domestic horse diverged from a common ancestor 500,000 years ago" ... "the only clearly distinctive difference between the two species was in the number of their chromosomes" ... "The P-horse has 66; the domestic horse, 64" ... "The close relationship, Lear said, "is reflected in the P-horse's ability to produce fertile offspring with domestic horses."
"If the wild horse mates with a domestic, the hybrid offspring will have only 65 chromosomes. But future generations will be back at 66 again."