  In analogy with the recently proposed lepton mixing sum rules, we derive
quark mixing sum rules for the case of hierarchical quark mass matrices with
1-3 texture zeros, in which the separate up and down type 1-3 mixing angles are
approximately zero, and $V_{ub}$ is generated from $V_{cb}$ as a result of 1-2
up type quark mixing. Using the sum rules, we discuss the phenomenological
viability of such textures, including up to four texture zeros, and show how
the right-angled unitarity triangle, i.e., $\alpha \approx 90^\circ$, can be
accounted for by a remarkably simple scheme involving real mass matrices apart
from a single element being purely imaginary. In the framework of grand unified
theories we show how the quark and lepton mixing sum rules may combine to yield
an accurate prediction for the reactor angle.
