Fertile Mare Mules*

A genetic study of esterase activity in mules, hinnies and their backcross progeny

“…For example, to explain the occasional fertility of a mule, Anderson (1939) originally suggested that only maternal chromosomes might segregate into the ovum, a full balanced horse set thus being recovered. This theme was more recently expanded by Chandley (1981) who suggested that chromosome segregation in mules and hinnies might be governed according to the principles of 'affinity', a phenomenon that gives complete or near-complete separation of whole parental genomes at meiosis in hybrids.…”

Fertile Mule in China and Her Unusual Foal

“…The vast majority of oocytes, however, fail at meiosis owing to the pairing problems encountered when the structurally different horse and donkey chromosome sets attempt to synapse at meiotic prophase. Anderson (1939) (Ryder et at. 1985).…”

The variety of sterility and gradual progression to fertility in hybrids of the horse and donkey

“…Since Anderson (1939) put forward his theory that the offspring of a female mule and a stallion was a horse, some have suggested that the offspring of female hinnies and jack donkeys should be donkeys (Chandley, 1981). Yet our findings indicate that this may not be the case (figs 16-19).…”

“…The hypothesis that the ova of fertile female mules and hinnies contain only a complete set of maternal chromosomes (Anderson, 1939;Chandley, 1981) provides one possible explanation for the production of a genetically balanced offspring to a fertile hybrid, but it does not deal with the question of the cause of fertility versus sterility. We believe that a new approach to the understanding of equine hybrid sterility is required.…”