There is another gene that is lethal homozygous. I want to say it is true roan, but I need to look up the sources again. Part of the confusion is there are several different varieties that are called "roan". Like pearl, it is lethal in utero.
Roan is not homozygous lethal in rats. You are probably thinking of Essex.
Last edited by Michelle.C; 11-14-2012 at 10:48 PM.