[Sverre Vigander]

Sverre Vigander  asked the Naked Scientists:
   
Hi,

I just listened to the November podcast of Naked Archeology, and I have a question about the Roman horse or donkey that was discussed early in the programme.

The extracted DNA was half horse, half donkey, and the possibilities that were presented on the show were all about how and where a contamination or analysis error could have occured.

Why not the obvious answer (to a lay person like me): Could it not have been a mule?

(I'm sure this was considered by the researchers, and probably immediately  discarded for reasons that are obvious to someone in the know, but the possibility wasn't even mentioned, so I thought I'd ask...)

Thanks again for a great podcast!

Regards,
Sverre Vigander, Norway

What do you think?

[CliffordK]

Equine genetics are pretty extraordinary that they can interbreed.

Modern horses have 64 chromosomes
Donkeys have 62 chromosomes
Zebras have either 32 or 46 chromosomes depending on the subspecies. 

So, a mule has half horse, half donkey chromosomes, and a total of 63 chromosomes. 
A zebroid will have either 48 or 55 chromosomes (32 horse + either 16 or 23 zebra).

The gene distribution on the chromosomes is slightly different too.

Meiosis with mules/zebroids is unstable, and you can't get a good set of chromosomes, and thus the animals are sterile.

So...
The problem is according to the show is that the DNA fragments had half horse, half donkey DNA.  However, a mule should have a 100% complete set of horse DNA, and every chromosome should have been intact when the animal was alive.  It should also have a 100% complete set of donkey DNA, and every chromosome should have been intact (2000 years ago).

If mules could breed, you could have crossovers.  But, since they are sterile, you shouldn't.

It sounds to me like they need to re-run the DNA.

[Mazurka]

My understanding is that whilst all male mules are sterile, not all female mules are.
I don't know if this helps!