In nature, cross-fertilization between animals is not uncommon, some spontaneously formed between animal groups, and some caused by human intervention.
In fact, in order to study the genetic mysteries of animals and the heritability of hybrid animals, humans have created many hybrid animals.
For example, the mating of two large and ferocious carnivores, tigers and lions, produces offspring, the former is born of the mating of male tigers and female lions, and the latter is produced by the mating of male lions and female tigers.
The hybrid zebra, a species obtained by hybridizing with any other equine, creates a unique family of hybrid zebras.
Of course, there are also some rare hybrid animals, such as grizzly polar bears, whales, leopard lions, prairie cats, mountain sheep and so on.
The emergence of hybrid animals helps humans understand the function of various genes in life, understand how life evolves, and some hybrid offspring fully inherit the excellent characteristics of both parents, which can provide people with labor or produce economic benefits.
However, some hybrid species, while having unique hybrid advantages, often come at some cost. The mule, common in the north of our country, is born of the mating of horses and donkeys, and combines the excellent qualities of its parents, but it is an innocent and pathetic animal.
<h1 class="pgc-h-arrow-right" data-track="17" > mule, horse, and donkey</h1> hybrid
Mules are the offspring of mating between horses and donkeys, and are a typical example of "hybrid advantage", with the characteristics of both horses and donkeys, mostly black-brown hair, stronger endurance than horses, and greater strength than donkeys. And longer life, docile temperament, hard work, from ancient times to the present has made great contributions to mankind.
Mules can not only tolerate extreme temperatures, but also can cross rugged mountain trails, and in some remote mountainous areas, mules are favored. Whenever the mule is mentioned, there are adjectives such as hard-working, generous and honest.
Mules are actually divided into two categories, one is a horse mule, which is the offspring of male donkeys and mares, and the other is a donkey mule, which is the offspring of stallions and female donkeys.
Due to the combination of cytoplasmic inheritance and genetic imprinting, horse mules and donkey mules have more or less differences in morphological structure, physiological characteristics, living habits, and even reproductive ability.
The shape of the horse mule is more like a horse, the bark is like a donkey, and the body shape and physical strength are slightly larger than the donkey mule. Since male donkeys and mares are easier to combine, the fertility rate is about 70-80%, and most mules actually refer to horse mules, which are very good servitudes.
Donkey mules resemble donkeys, bark like horses, are smaller, and eat less than horses and mules, but they are better at running than donkeys. The union of male and female donkey cells is a small probability event, with a fertility rate of only about 30%, compared to the number of donkey mules.
Mules have a taller body, stronger physique, and tougher endurance than their parents, which fully demonstrates the charm of mixed race.
Unfortunately, mules are usually unable to reproduce, and from an evolutionary point of view, these good genes do not last forever.
<h1 class="pgc-h-arrow-right" data-track="106" > mules are male and female, but highly sterile</h1>
Mules have reproductive organs and male and female, but they cannot reproduce offspring, and mules, which are widely used as slave animals, can only be obtained through interspecific hybridization of horses and donkeys, not through intraspecific mating. Why can't mules have children? In the final analysis, it is the "horse and donkey" that causes it!
Most people probably understand that mules are infertile because horses and donkeys are not the same animal and produce offspring that cannot be produced.
In fact, horses and donkeys belong to the mammalian-odd-hoofed order-horse family-horse genus, and have a common origin, but different species. The inability of their offspring to mate involves a biological hybridization problem.
We know that the vast majority of mammals are produced by mating between females and males, and that viable sex cells (males call sperm, females call eggs) are formed by meiosis.
Germ cell chromosomes are half of the somatic chromosomes, while higher animals are developed from fertilized eggs, and half of the chromosomes in the body come from the father (sperm) and half from the mother (egg).
When horses and donkeys mate, the reproductive cells of both sexes combine to form fertilized eggs, and the fertilized eggs divide and differentiate to develop into mules. Therefore, the number of chromosomes within mule body cells is determined by the chromosomes of horses and donkeys.
The point is that the number of chromosomes for horses is 64, or 32 pairs, and the number of chromosomes for donkeys is 62, or 31 pairs; then the number of chromosomes for mules is 63 (32 from horses and 31 from donkeys).
When the mule is about to give birth, it must first undergo meiosis to form normal sperm and eggs, and after the association is paired (that is, homologous chromosome pairing), but the mule's chromosomes are odd, there is no homologous chromosome in the body, and normal meiosis cannot be performed.
This creates confusion about chromosome pairing, and in any case there will always be a chromosome that is lonely and cannot form normal germ cells, so mules generally cannot produce offspring.
<h1 class="pgc-h-arrow-right" data-track="108" > mule pregnant must die, is it true? </h1>
Mules, which are not horses and non-donkeys, usually do not have the ability to reproduce, and in the eyes of most people, mules are "extinct" animals. However, the world is so big that nothing is completely absolute, and a very few female mules mated with stallions or male donkeys and are fertile.
Mule cubs have been reported in the domestic and foreign media, and since the establishment of relevant archives by humans in 1527, at least 60 cases have been recorded in ancient and modern China and abroad.
In china's ancient books, the offspring produced by the male horse with the female mule are called the horse (jū), and the offspring born of the male donkey with the female mule are called the horse (xū).
Since mules are highly sterile, why are there any cases of mules laying down? In fact, this is a very unlikely event.
After the mule is sexually mature, the sex cells into which the chromosomes are divided are completely random, and when a sufficient amount of female mules mate with a stallion or male donkey, there may be a chance to form normal sex cells.
This phenomenon is rare, the odds are quite low, theoretically only about one in four billion, but in fact it will be lower. In life, only a very small number of female mules can lay cubs, while male mules cannot produce sperm and have no reproductive ability at all.
Because the phenomenon of mules giving birth to cubs is extremely rare, it is difficult to see a case for decades or even hundreds of years, and the ancients lacked understanding of it, and it happens that a very small number of fertile female mules are pregnant, and they will unconsciously associate with "disaster coming".
Out of fear, some people think that mule pregnancy is against common sense, not a good thing, and even secretly dispose of the mother mule, so there is also the saying that "mule pregnancy must die".
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