Quote:
Originally Posted by tore
When two organisms that are very dissimilar create a hybrid (f.ex horse and donkey), the diploid mule offspring's cells can have two very different sets of chromosomes. When meiosis is to take place in the hybrid, chromosomes can have a hard time pairing up with their homologues from the other dad/mum set or the mixing between them creates problems .. possibly because their homologues in the other set are so different or even because they're simply not present! Horses and Donkeys have different amount of chromosomes which would result in some chromosomes being unable to pair up with homologues. This can cause a multitude of problems, many which end in reduced ability to reproduce and even sterility.
I'm not sure if that made it understandable. Possibly, this meiosis illustration might help a little bit. 
edit :
Gurgh, had to brush up a bit on that explanation. I think it's understandable now. 
edit 2 :
By the way, some "species" do hybridize quite a lot in nature, for example many birds. Hybrids are not always sterile, but may simply have lower reproductive ability which translates to lower fitness. |
I didn't even think about the bolded. I feel stupid for not realizing something as important as that. I'm assuming either horse or donkey has more information than the other, leaving spare chromatids over? I never learned any of this during school, I'm just guessing btw. So if two animals in a similar situation to horse and donkey reproduced but had an equal number of chromosomes the product would be fertile? Or would the only time this happened be within the same species? Meaning that in every circumstance different species never have an equal number of chromosomes? I think I may be complicating things.