Why and how are mules sterile?

Question

Is it because all mules are a certain sex, or they don't have reproductive organs?

Answer 1

First thing you have to realise is that all mules are NOT sterile. Most mules certainly are, but there have been numerous authenticated accounts of mules giving birth to perfectly healthy foals.

Next thing to do is to ignore those people saying that it is because they are hybrids or because horses and donkeys are different species. Numerous species are perfectly interfertile despite being far more distantly related than horses and donkeys and having far more widely differing chromosomes numbers.

Thirdly ignore those people saying that mules are clones. Mules are the product of sexual reporduction. If they were clones then by definition they would be either entirely horses or entirely donkeys.

And finally mules have perfectly functional reproductive organs so that isn't the reaosn.

So why are mules sterile?

That’s pretty complicated and to be quite honest we still don’t know the whole story. The basic problem is that after the ancestors of donkeys and horses split the chromosomes of BOTH species fused and then those fused chromosomes re-split. That has led to a situation where the information originally carried on a single chromosome in the ancestral species is now found on 2 different chromosomes in mules and 2 totally unrelated chromosomes in horses.

Normally a developing foal embryo would receive two copies of each piece of genetic information: one from the mother and one from the father. In the case of a mule foal it receives a random number of copies. It will receive three copies of some pieces of information: 2 from the mule parent and one from the horse/donkey parent, or it will receive only a single copy from the horse/donkey parent.

Because of that mismatch of genetic material the embryo has a hard time developing. Some traits it will lack sufficient information for since it has only half the required genetic information, while other traits will be overdeveloped because there are 3 or more genes where there should be only two. All mules will get pregnant if mated, but the embryo develops for just a few days and then dies because it lacks the correct genetic instruction to develop further.

As for why some mules, maybe one in a thousand, are fertile, nobody is quite sure.

Answer 2

A Mule is a cross between a Donkey and a Horse. As with most Hybrids this causes chromosome damage. In order to have sexual reproduction chromosomes are exchanged, so if they are damaged then no reproduction. Long Stem Roses are the same in that they are a hybrid and are sterile.

Answer 3

No, it's something about them being a "hybrid." I read that in some rare instances mules have given birth. My grandpa tried his best to figure out a way to explain it to me when I was a little girl. He grew up on a farm and was always telling me stories about horses and donkeys and mules. I said something about a daddy, mommy and baby mule and he said, No, a horse and donkey parents make baby mules. I was so confused and he was laughing and I think he got a big kick out of it but at the time I just could not understand.

Answer 4

This Site Might Help You.

RE:
Why and how are mules sterile?
Is it because all mules are a certain sex, or they don't have reproductive organs?

Answer 5

History and Origin of the Breed

Under conditions of domestication it is possible to obtain hybrids between equid species. There are records of onager/***, onager/horse and zebra/horse (zebroids) crosses, but the cross that has been most significant in human history is one between horses and donkeys. Breeding a male donkey to a female horse results in a mule; breeding a male horse to a female donkey produces a hinny.

Offspring from either cross, although fully developed as males or females, are almost always sterile. Hence, a line of horses and a line of domestic asses must be maintained to perpetuate mule or hinny production

Answer 6

What Are Mules

Answer 7

Horses and donkeys have different numbers of chromosomes. When they try to make gametes, there are errors during meiosis that result in inviable offspring.

However, mules have produced babies from ttime to time.

Answer 8

Mules are a cross breed of Donkey and Horse... and because of the genetic makeup they are unable to produce offspring.

Answer 9

They are a hybrid animal. The product of a horse and donkey. Just some quirky thing about nature...

Answer 10

Because a mule is the product of breeding two different species. They are a hybrid, and most hybrids do not have the ability to reproduce.