Horse, donkey, and zebra karyotypes

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Evolutionary movement of centromeres in horse, donkey, and zebra:

Centromere repositioning (CR) is a recently discovered biological phenomenon consisting of the emergence of a new centromere along a chromosome and the inactivation of the old one…Even more surprisingly, five cases of CR have occurred in the donkey after its divergence from zebra, that is, in a very short evolutionary time (approximately 1 million years).These findings suggest that in some species the CR phenomenon could have played an important role in karyotype shaping, with potential consequences on population dynamics and speciation.

I though this was interesting because a) I don’t know much about higher order genetic changes (chromosomal rearrangements, etc.) b) we’ve talked about chromosome # differences between wild and domestic horses before (they are full interfertile). Anyway, I know aneuploidy is usually the problem, but I think there will be some really interesting stuff coming out of this area (I wonder if RPM could offer more?).


  1. Centromeric shifts often follow Robertsonian fusions. Rachel O’Neill is one of the leaders in this field — she studies the phenomenon in marsupials (where it has been associated with speciation). Also, it appears that hybridization between different karyotypes can induce centromere relocation in marsupials. Don’t know much about horses, though. 
    I, actually, don’t think aneuploidy is that big of a deal. I think the rearrangements suppress genetic flux between karyotypes allowing for the accumulation of genetic isolating factors on rearranged chromosomes. This is the case in Drosophila, and has not been rejected in mammals.

  2. I don’t know anything about it, but it makes one wonder if this changes the type of new genetic combinations that can occur during meiosis due to crossing over if there is some minimum distance from the centromere at which crossing over can occur.