Reproductive isolation from a cross between a horse and a donkey or between a mare and a donkey, respectively. These animals are nearly always sterile due to the difference in the number of chromosomes between the two parent species. Both horses and donkeys belong to the genus "Equus", but "Equus caballus" has 64 chromosomes, while "Equus asinus" only has 62. A cross will produce offspring (mule or hinny) with 63 chromosomes, that will not form pairs, which means that they do not divide in a balanced manner during meiosis. In the wild, the horses and donkeys ignore each other and do not
Equus (magazine) Carrying the slogan, "The horse owner's resource", "Equus" is meant to be collected by subscribers so they might use articles in past issues as a reference. Each issue has a prominent issue identification number on the cover (e.g., the June 2005 issue is ""Equus" 332"), and an index to articles is published annually. After the June 1998 sale of Shinitzky's Fleet Street Publishing to PRIMEDIA, the magazine was published by the PRIMEDIA Equine Group. From 2007 to 2010, with the completion of the sale of the PRIMEDIA Enthusiast Media group, the publisher was Source Interlink. Since 2010, "Equus" has been