Beyond the physiological, hinnies and mules differ in temperament despite sharing nuclear genomes. Mules are much more common than hinnies. Physical differences between hinnies and mules are not restricted to stature. Like other inter-species hybrids, mules and hinnies are usually sterile. Just as male mules and hinnies are infertile so are male zebroids. Hinnies are rare for many other reasons. Like mules, hinnies express broad variation in stature. The stallions are often crossed with female donkeys (Jennies) to produce hinnies. Hinnies are the reciprocal cross to the more common mule.