What does this description of the C57BL/6J mouse strain mean? - (Jul/29/2012 )

Looking up this mouse strain, I found this website (http://jaxmice.jax.org/strain/000664.html) describing the strain as one providing a
"permissive background for maximal expression of most mutations"

What does this mean?
Do any of you know the molecular/genetic basis of creating a mouse that allows this?
Do you know any good papers/references which might answer my question?

I'm just a curious undergraduate...

Jax (Jackson laboratories) is the biggest (and best) lab animal breeding organization in the world. If you read the notes carefully, you will note that it is a spontaneous mutation and that it was bred by crossing siblings. C57 black mice are very common in many labs around the world.

A permissive background is one that allows expression of the mutation without adverse affects on the animal to a large extent. It may also mean that there is a limited capability to repair the genome, or something similar. I don't know the genetic basis for it at all.

For refs, try the ones starting about 2/3 of the way down the page.