You can always edit your post if you want:)
As far as I know, Jill Rees line does not have the White Sport gene. Only line A or B had them. Someone correct me if I am wrong!
So if you are going to cross a Jill Rees roo with a line C Legbar, your chances of getting a White Sport will be zero.
Yes, I did say the GFF A before but have corrected it now. I want to make sure I state my birds correctly especially when I ask a gazillion questions about them.
You are probably very correct about the Jill Rees lack of the white genetics. It is a shame though for me. One of my friends has a GFF C roo, if I have stated that correctly. She got hers when GFF started selling their lines in order to bring in the Jill Rees. She has never gotten a white chick though so maybe only the A & B lines had the genetics to produce one unless bred into them later.
Locally here a lot of people have the GFF lines but they are now breeding them with the Jill Rees lines and getting quite a bit of color disparity in their birds, even when they are the same sex, just as others here are getting with their GFF lines with no Jill Rees birds in their flocks.