User blog comment:Xilinoc/Ch. 543 - Letters/@comment-5462417-20130627023954/@comment-11051098-20130627071428

As far as I understood, the Ishida family was from a very strong line of Quincies. Even though Katagiri was a mixed-blood Quincy, Uryû could have become a full-blood.

Someone wrote in another topic, concerning genetics passing from parent to child, that as a full-blood, Ryûken's Quincy genetics could be symbolized as QQ, being an Echt, and Katagiri's genetics Qq as a Gemischt. They would each pass down one gene to Uryû.

Judging from that, Uryû would either be a Gemischt (Qq) or an Echt (QQ) Quincy. He would obviously get Q from his father, but there is a chance he could have gotten the Q gene from his mother as well, there is a 50-50 chance for that, genetic-wise.

I would assume it's either that, becoming a full-blood because his father's Quincy heritage is very strong, or something else we don't know about yet.