can't get homozygous mice, why? - (Jun/12/2009 )

Are they Tg or Knockout mice? (here in Aust we tend to use -/- for KO as it represents null)? However if you are not transferring onto a different background, and you say you have het parents and these mice have bred previously and all you get is +/+, then according to simple mendelian genetics, your parents would have to be both +/+.

I would check your primers and re-test your parents.

Good luck

My question is on which chromosome is the knock out mutation???
If it's on the X chromosome your males are hemizygote and potentially sterile...happened to me.
Either due to the mutation or just simply since you disrupted the X chromosome where a lot of spermatozyte maturation genes are encoded.
My bet..if it is on the X ..check by IHC for mature spermatocytes!!
Good luck!