How Do Mules Reproduce? A Detailed Explanation of the Principles

A mule is a hybrid of a donkey and a horse, with strong vitality, a sturdy constitution, and easy handling; it can be used for work for 20 to 30 years. So how do mules reproduce?

1. How do mules reproduce?

Mules are produced by crossing a male donkey and a female horse. The two have reproductive isolation and cannot reproduce offspring. The main reason is that the chromosomes of mules do not come in pairs, so germ cells cannot undergo normal division, and they are basically unable to reproduce offspring.

2. Why are mules infertile?

1. Whether it is a horse mule or a donkey mule, their chromosome numbers are not quite normal. This is because donkey chromosome 2 is homologous to horse chromosome 1, donkey 13 to horse 11, and donkey 14 to horse 13. Donkey 16 plus donkey 25 together correspond to horse 5, and the horse has 32 pairs of chromosomes, while the donkey has 31 pairs. Although horses and donkeys are relatively closely related, their gametes can not only combine with each other but can also develop into complete individuals, yet the number of chromosomes in the cells of their offspring becomes 32+31. No matter what, there is always one chromosome left alone.

2. Still, mules are fortunate, because if this were the number of chromosomes in the cells of a certain horse (if it were a horse, it would be called monosomy 2n-1), it would basically be unable to survive. For sexually reproducing diploid species, the survival ability of pure haploids is even better than this state. Conversely, if this were the chromosome composition in the cells of a donkey, it would become trisomy, and the extra chromosome would certainly be present in three copies. A mule with 32+31 is not truly a relationship of 31 pairs + 1. That is to say, during meiosis, it will not simply separate the 31 pairs of chromosomes from each other and then randomly assign the extra one. This is the trouble encountered by mules and other hybrid animals: during the process of chromosome separation, their chromosomes tend to separate randomly and assort independently. Because for trisomies that can survive, although their fertility is lower than normal, it is still quite high; apart from that extra chromosome, all the rest can pair normally and separate from each other.

3. For the unfortunate mule (taking a female mule as an example), what is the chance of producing a normal egg? For example, in an extreme case, its egg happens to contain 31 chromosomes from the donkey, or 32 chromosomes from the horse. Obviously, such a probability is quite low (interested comrades can calculate it). Of course, the actual situation does not need to be so extreme. After all, the mule itself can survive, which means the egg can contain a harmonious combination of horse and donkey chromosomes.