I am characterizing a new transgenic mouse line with an interesting phenotype. The F2 generation started at about 50% transgene positive, with decreased inheritance as each litter progressed. The F3's started at over 80% positive and also decreased each litter. (The litter size doesn't decrease, just the percentage of transgene positive mice.) My guess is that we have some defect in germ cell development, but I'm having trouble finding similar phenotypes in the literature. Any suggestions as to what's going on here? Thanks!