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 lambei Equus lambei Equus lambei (common names include Yukon horse, and Yukon wild horse) is an extinct species of the genus "Equus". "Equus lambei" ranged across North America until approximately 10,000 years ago. Based on recent examinations of the mtDNA of "Equus lambei" remains, scientists have concluded that "E. lambei" was probably much like the extinct Tarpan, also known as the Eurasian wild horse, and the living Przewalski's Horse. A partial carcass of "Equus lambei" is on display at the Yukon Beringia Interpretive Centre in Whitehorse, Yukon. Evidence from "E. lambei" mtDNA has shown that "Equus lambei" is a close relative