Female bred twice only 1 pup survived

I have a female hooded rat that I bred twice now. The first breeding, she had 12 pups but I found all but one of them dead. I put the survivor with her sister's pups and it survived. The female in question did not seen to care for her pup whatsoever. Anyhow, I thought I'd wait a couple of months and try her again to see if this was just a fluke litter. This time 7 pups, all dead. Anyone else ever have this happen? There seems to be nothing wrong with the developement of the dead pups, and she is healthy. Well, she is officially retired. She poses no threat to her sisters litters and I will just keep her to keep her sister company (besides my oldest daughter took a liking to her and would never let me feed her off to my snakes.).

Your pairing could easily be resulting in a lethal gene. Might want to do research on the rat colors.

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Originally Posted by Raptor

Your pairing could easily be resulting in a lethal gene. Might want to do research on the rat colors.

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Hmmm...bred her to another hooded rat. Was a tan hooded and she is a black hooded. Didn't think that would cause any issues. But I'll keep that in mind.

In a lot of cases it's the actual pattern. I went and found this website:
http://www.curiosityrats.com/geneticsmarkings.html

You could breed her to a different male (if you haven't already). If you have bred her to two different males, it might be best to cull her.

I will try her to one other male that I have and see if I get better results. Thanks for the info.