The genes of male and female donkeys are easier to combine, so most mules cross in this way. However, the chance of gene combination is still small: it took some horses six years to successfully mate and get the donkey pregnant. Males and most denominator mules are born infertile. There is no fertility because the two species have different chromosome numbers: donkeys have 62 chromosomes and horses have 64 chromosomes. The female mule has sexual function, and the uterus can be pregnant with embryos, but the most difficult thing is to get the female donkey pregnant.
Mules, as interspecific hybrids (including beards between male donkeys and female donkeys, mules between male donkeys and female donkeys), are generally infertile. However, at all times and in all countries, there are many female mules and beards who meet Ikoma by chance, and of course, they can also meet their backcross generation, that is, B 1. In China ancient books, the offspring of a male horse with a female mule is called a raccoon, and the offspring of a male donkey with a female mule is called a raccoon. The typical example of China mule Ikoma is the report that Zong Enze and others have systematically studied for many years. * * * The quantity is about 13, so I won't repeat it here. The related case reports of Ikoma, a foreign mule, are introduced as follows for Chinese reference.
The earliest record abroad is a book written by Herodotus and translated by Russian husband. Gormishenko in 1888 —— Historical stories in nine books. When Babylon was besieged by the Persian Empire around 600 BC, in order to ensure the food supply for the war, a female mule accidentally gave birth to a pony halfway.
1992, Zeiler wrote in the relevant chapter of German Yearbook of Animal Husbandry Science and Technology, 1759, a mule born to a mare gave birth to a mule colt, but the mule colt is very similar to the colt in appearance. It is also written that in Valencia in 1762, a mule born to an Andalusian mare gave birth to six offspring (B 1) in her life, and these offspring are no different from the foal in appearance. The author also reported that in 1873, a male horse and a female mule gave birth to offspring in Arghir. Most notably, the author also reported an example, that is, in an experimental station in Tripoli, a female mule named "Moore" mated with an Arabian stallion and gave birth to two mules and ponies that looked like ponies. Later, she mated with "Moore" and a male donkey and gave birth to two ponies. However, the twins born this time are typical mules in appearance.
In 19 16 "German Yearbook of Animal Husbandry Science and Technology", Deschambre reported that 1 Egyptian white donkey was found in Bruen, France, and gave birth to five foals (B 1), three of which were from Berber stallions. The first three horses are called Kumir, Constantine and Genpupian. They are no different from horses in appearance, and they are all fertile. The latter two are typical mules and can't bear children. Deschambre also mentioned in the article that as far back as 1898, there was also a case of Ikoma, a female mule.
1928, A.R.Groth reported in the Journal of Genetics that a female mule named "Alder Baker" of Texas Agricultural College in the United States gave birth to a stallion by mating with a stallion riding in 1923 (B 1). It is worth noting that this stallion born by a mule has normal sexual function as an adult, and mated with two mares in 1926. One of them got pregnant and gave birth to a foal that looks like a mare (B2). Later, several mares were bred and a male foal was born (B2). Their offspring are all fertile.
The author also wrote that "Aldeback", a female mule, mated with a male donkey in 19 19 and gave birth to offspring, but her appearance was typical and she was infertile. 1924, the male donkey mated again. Although she was pregnant, she later had a miscarriage.
Warren (A.Warren, 1926) once reported that in 1924, a female mule named "Firth" in South Africa gave birth to a pony with the same appearance as a horse. Seven years later, the pony mated with the stallion in estrus and gave birth to a pony, which looks just like a horse.
1939, W.S. Anderson reported in the Journal of Genetics that a female mule mated with a Bell Snow Dragon stallion and gave birth to a pony, which had all the characteristics of her father's Bell Snow Dragon stallion, but none of the characteristics of her grandfather's donkey.
There are many reports about mule Ikoma abroad. For example, Mueller reported that a mule Ikoma happened in Esten, Africa in 1903. Harveu once reported that in 19 13, a female mule mated with a male donkey and gave birth to a male donkey. The following year, she mated in estrus (still with a male donkey) and gave birth to another female donkey. Montpair once reported that in Morocco 1923, a female snail mated with a riding Berber stallion and gave birth to a pony, which looks like her father, Berber Horse. Lawrence once reported that 1927 in Nebraska, a female mule mated with a male donkey and gave birth to a pony. H.Smith once reported that in 1939, Arizona, USA, a female mule mated with a male donkey and gave birth to a pony, which was exactly the same as her female mule.
From the above case of mule Ikoma, it seems that the following impression can be given:
(1) As an interspecific hybrid, a few mules (including beards) are fertile;
(2) A few fertile female mules can give birth to offspring by mating with male horses or donkeys (b1);
(3) B 1 born when backcrossing with male donkeys not only has the typical appearance characteristics of mules, but also is infertile;
(4) B 1, which is born from the backcrossing between the female mule and the male horse, is not only identical in appearance to the horse, but also fertile for both sexes, and B2 is completely the appearance and physical characteristics of the horse;
According to the above points, it seems to prove Anderson's regression theory. However, in order to confirm the regression theory, karyotype analysis is needed.