in breeding dal X dal cavies the double up of the dal gene, much like a the male brindles has the same effect. In cavies the babies with deformaties are call anothalmic or microthalmic whites (or something with similar names, tis hard to spell!). theyre born with pink eyes, if they have any at all, and are white. deformaties include no teeth, no organs ect, most die without having to cull (and this type of thing being born is the only reason a cavy breeder would cull, as cavies are born fully developed)
this is avoided in cavies by using selfs though. However i know you cant get over it that easy in mice since its sex linked, but maybe one day a buck will be born without this lethal outcome? never know when mutations will appear in the genes. but untill then, what has to be done, has to be done!!