Precise tests of a quark mass texture

The relations $|V_{ub}/V_{cb}|=(m_u/m_c)^{1/2}$ and $|V_{td}/V_{ts}|=(m_d/m_s)^{1/2}$ between the CKM matrix elements and the quark masses are shown to imply a remarkably precise determination of the CKM unitarity triangle or of the Wolfenstein parameters $\rho$, $\eta$ consistent with the data so far. We view this as a clean test of a quark mass texture neatly arising from a hierarchical breaking of a U(2) flavour symmetry.