Mules . . What Does it all mean?

[Dr. Dalek]

Hi everybody.

It has been awhile since I posted. I have been busy with school.

 

Anyway I was doing some reading online and I found something interesting. Apparently Mules which are the hybrids of Donkeys and Horses and are normally sterile and are so because of their odd number of chromosomes.

Since Horses have 64 chromosomes and donkeys have 62 the mule has 63. When they try to breed the differing numbers of chromosomes don't match up with the gametes of the other mule and they fail to breed. I know there may be more too it than that however for simplicity sake this is all I will share on the matter.

However if a female mule is bred with a pure horse or a pure donkey there can occasionally be offspring from this union. This has been documented and observed several times and even confirmed with genetic testing on one occasion.

From what I have read this is said to occur occasionally because haploid gametes of the mule can have (on occasion) the appropriate number of chromosomes to match up with the gametes of either a pure horses or a pure donkey. However the circumstances have to be just right as to what gametes meet or the zygote will not form.

Morocco's miracle mule.

 

I am wondering if this is true can the offspring of the mules breed? If so this means that there can be genetic drift between horses and donkeys because of chromosomal crossing over during gamete formation.

 

Someone I know asserted that this could not happen and that the offspring of the mules would be sterile. He gave to reason why this would be the case. If they had an even number of chromosomes (which must be the case because how else could they be born?) I don't see why they wouldn't. He simply asserted that he knew it was true and cited his high marks in AP Biology in high school (Nothing I haven't done as well) as evidence for his authority on the matter.

 

Is there another aspect to this puzzle that would prevent the offspring of mules from breeding besides chromosome number. I know that the proteins around an ova are supposed to be selective to sperm and only allow the sperm of similar species to pass into the ova. However I do not see why this would be the case. If donkeys and horses were dissimilar enough to block out each others gametes there would be no mules in the first place. Does anyone have any information on this matter?

[Mokele]

A mule has 63 chromosomes. It may, on rare occasions, produce a gamete with 62 (like a donkey) or 64 (like a horse). Those gametes combine with either horses or donkeys, the result will be another mule, but it's only got a 50/50 chance of being fertile. If it produces a 64 gamete, but mates with a donkey (62), you'll get a 63 offspring, a regular sterile mule. But if it produces a 64 gamete and mates with a horse (also 64), the offspring would have 64 chromosomes and be fully fertile.

 

There can be gene flow between species due to hybrids. This has actually been observed in Darwin's finches, as well as other species. In fact, fertile hybrids aren't that uncommon.

[ebayandres]

Just to add a note... I read that the Lion Tiger hybrid produces fertile females and sterile males.

[Mr Skeptic]

He simply asserted that he knew it was true and cited his high marks in AP Biology in high school (Nothing I haven't done as well) as evidence for his authority on the matter.

 

Well, tell him I say lol.