It said on the Animal Planet “The Most Extreme Births” segment that in Naked Mole Rat colonies the naked mole rat “queen” breeds with her eldest sons and keeps daughters from ovulating with pheromone controls (like some eusocial insects).
I thought incest was a genetic negative in all mammals. Why the exception for mole rats?
You want a genetice penalty beyond being a naked mole rat?
No genetic penalty? Have you seen them? They all look like the kid from Deliverance.
Dunno, honestly.
However apparently some are of the opinion that in-breeding is perhaps not so common in Naked Mole Rats after all ( note the references on this page ):
http://www.biology.wustl.edu/templeton/people/jon/
If there is a viciously effective mechanism to eliminate defectives, then while inbreeding my produce defectives, such defectives will not live long enough to breed. This will eliminate many problems, leaving only the genetically healthy to survive.
Well, I don’t know about “no penalty”…before they started practicing incest, they were a subspecies of wolf. 
Thank you, Broomstick, for your good response. Inbreeding would produce no “genetic penalties” were the population willing to cull out the defective offspring. IIRC, something like this system was employed on the island of Hawai’i in times past, where the highly incestuous natives used infanticide to rid themselves of any deformed or sickly children, leaving only the healthy to survive and breed in turn. Chlorinating the gene pool, if you will.
As our modern-day culture is a little squeamish about infanticide, we find it best just to outlaw incest entirely. 
.:Nichol:.
Incest doesn’t produce any new bad genetic stuff - it only makes it more likely that bad recessive genes will be expressed. If you weed out all of those genes, there’s nothing negative about incest. Not being intimately familiar with the sex lives of naked mole rats (and I call myself a Doper!), I can’t really say for sure what’s going on with them.
They cull (or once culled) weak and sick animals.
The queen only mates with the best of her sons (and she had to mate with someone not her son first, to produce them, right?)
So many years have passed, they are probably homozygous for good recessive and dominant genes, having eliminated the bad genes generations earlier.
Incest doesn’t necessarily produce anything bad at all - even over long periods in humans either. Cleopatra - yeah ** that ** Cleopatra - was the product of 17 generations of brother - sister marriage.
Just food for thought…
