There is such a creature, which is basically incapable of fertility, but has a long history of survival, and is still "working" for people today. Do you know who this creature is talking about?
It is the crystallization of the love of a horse and a donkey".mules".It inherits many advantages of both parents, but it is difficult to achieve natural reproduction by ability.
Mules inherit many of the advantages of horses and donkeys, but it is difficult for them to breed naturally.
So, what are the characteristics of a mule? What are the advantages of horses and donkeys? And why is it said that it is infertile?
Ever since people mastered the art of hybridization, they have always liked to create strange "fusion species", such as ligers. However, these artificial hybrids are not in good health, and they seem to be extremely painful when they are alive.
Of course, one creature that has been particularly successful among the many failed works is the mule that has accompanied humans for many years. According to the information,As early as 4,000 years ago, our ancestors mastered the art of making horses and donkeys perfectly cross and eventually produce mules. At that time, in Xinjiang, Gansu, Inner Mongolia and other regions of China, mules appeared.
Mules are the offspring of a cross between a horse and a donkey.
It is worth mentioning that at that time, the names of mules were already divided into two types. If it is born of a combination of a male donkey and a mare, it is calledHorse mules, in the case of gender reversalDonkey and mule。There are some differences between horse mules and donkey mules, but they are not obvious.
However, when you compare a mule with a horse and a donkey, the difference is more obvious. It is of moderate size, smaller than a horse but larger than a donkey, and its ears are significantly longer than those of a horse, but they are still far from the length of a donkey's ears。Many people think that in terms of appearance, the mule will be more like a donkey, because it looks shorter and less slender than a horse. Again,The sound of a mule is also more like that of a donkey.
Compared with horses and donkeys, mules are a little more like donkeys in appearance.
However, for the people who created mules at that time, the shape was not important, what mattered was whether the mule was better or not. The mule does have many characteristics, not only is it not a picky eater, but it is also very resistant to disease and adaptable.
What's more,This guy's stamina value is off the charts, and his lifespan can often reach about 35 years old。Because of this, many people at that time used mules as their main vehicles to carry goods for themselves. In addition, in terms of personality alone, the mule is also better. It is not as stubborn as a horse, more docile than a donkey, and prefers to stay with its companions.
Mules used to be the main vehicle of the people, and their personalities were more docile than donkeys.
In this way, the mule is indeed one of the most successful hybrids of all time, perfectly inheriting the advantages of horses and donkeys, making itself so good. For the people of the time, it was simply the best vehicle.
But there is nothing perfect in this world, and although the advantages of mules are very numerous, there is also a fatal shortcoming, that is, they are unable to have children.
There is no way for mules to breed naturally.
As a sexually reproducing organism, the mule must rely on the mating of both females and males for its reproduction. From a biological point of view, this mating is all about allowing the germ cells of both sides to meet and combine and eventually produce offspring.
In general, both female and male germ cells pass throughMinuses**The way of formation, because of this, in the processThe number of chromosomes in germ cells tends to be halved, and only 1 2 of the number of chromosomes in maternal cells is reduced
The process of biological germ cell meiosis**.
Looking at the chromosomes of both parents of the mule, the horse has 64 chromosomes, and the donkey has two fewer chromosomes, 62. This means that the reproductive cells of horses have 32 chromosomes and those of donkeys have 31. Once the two of them are combined, the two germ cells will meet and combine to form a fertilized egg, and the number of chromosomes in the fertilized egg is the sum of both sides.
This means that regardless of whether the horse or the donkey is male or female, the number of chromosomes left in the mule will be the same63 articles
The number of chromosomes in a mule is 63.
The number 63 is very embarrassing, because the minus of germ cells often has two subsides, and each time it goes through four stages. In the phase, homologous chromosomes pair with each other and then move to the poles of the cell.
When the first meiosis** ends, 2 daughter cells are formed, and these 2 daughter cells (also called secondary blasts) form 4 sperm or 1 egg and 3 polar bodies after the second meiosis**, and the polar bodies are cells with only nucleus and almost no cytoplasm, and finally disappear and have no heritability.It stands to reason that if they can be paired eventually, healthy germ cells can be formed. However, the number of homologous chromosomes belonging to horses and donkeys in mules is different, with 32 belonging to horses and only 31 belonging to donkeys. Because of this, no matter how you match it, you can only match 31 pairs.
The number of chromosomes in the body of a mule that belongs to a donkey and to a horse is different.
The remaining "single dog" chromosome will always be the "widow king", andIts presence also renders the entire germ cell incapable of normalizing**, eventually rendering the mule incapacitated. It can be seen that horses and donkeys are indeed mainly responsible for the fact that mules cannot have children, and it is their different chromosome numbers that are to blame!
It is worth mentioning that although objectively speaking, the vast majority of mules are infertile, there are also some individuals with "skeletal surprises". Over the years, there have been news of mules giving birth to offspring, but it is usually the mother mule who is pregnant, and it is certainly not a male mule that is mated with her, but a healthy horse or donkey.
If a mule mates with a horse or donkey, the offspring have chromosome distribution.
At this point, one might argue that the claim that mules are infertile is false, but the premise of this statement is that both parties are mules and give birth to offspring in the case of natural mating, rather than continuing to cross with other breeds of animals.
As for why female mules can get pregnant, male mules can't leave offspring, mainly becauseEquine fertilization sites are more special, all in the ampulla of the fallopian tubes。This means that before the sperm reaches its destination, it needs to go through layers of obstacles. The male mule's ** is very thin, and the germ cells are unhealthy and have no vitality. In this case, it is even more difficult for it to break through than to climb to the sky.
Unlike other equine animals, male mules are unable to leave offspring.
The female mule is relatively easy, just waiting for the sperm to arrive at the door, and then pairing with the egg cells. Rarely, the chromosomal union in the female mule's body can be successful and thus function normally.
At this time, after coming into contact with another normal germ cell, it will naturally be able to reproduce smoothly. It should be noted, thoughThis probability is still very low, only about a few in 10,000, which is extremely rare.
The chances of a mule being able to conceive successfully are very low.
In addition to that,Even if a mother mule is pregnant, it is still difficult to give birth to offspring on her ownThis is why there is a saying that "a mule must die if it is pregnant".
According to the data, the pelvic bones of the mule are very narrow and basically cannot be opened and closed, which makes it difficult for the fetus to be born after maturity. At this time, it is necessary to rely on people's intervention to achieve "mother and child peace". Because of this, if a female mule is successfully pregnant in the wild, then it faces a certain death, often one corpse and two lives.
Even if a female mule is pregnant, it is very difficult to give birth smoothly.
Overall, the fertility problem of mules has not been solved to this day, and with the replacement of traditional vehicles, the demand for mules is not as high. In the long run, the mule may gradually disappear into the human world, which is indeed a bit regrettable.