Horse breed been produced. Such restrictions have led to legal challenges in the United States, sometime based on state law and sometimes based on antitrust laws. Horses can crossbreed with other equine species to produce hybrids. These hybrid types are not breeds, but they resemble breeds in that crosses between certain horse breeds and other equine species produce characteristic offspring. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, the hinny, is a cross between a stallion and a jenny (female donkey). Most other hybrids involve the zebra (see Zebroid). With
Social groups in male and female prisons in the United States point. This difference is a manifestation of gendered social factors which influence male and female populations within prisons and within larger society. The populations and demographics of male and female inmate populations in the US are very different from one another. These differences factor heavily into theories on prisoner social organization. The most significant difference is in the relative size of male and female populations; in 2014 there were approximately 1,440,000 male and 112,000 female prisoners in the United States. The much larger size of the male prison population causes major differences in the institutions in which male and female