[en] In this paper, a new ansatz for quark and lepton mass matrices is proposed in the context of supersymmetric grand unified theories. The 13 parameters describing fermion masses and mixings are determined in terms of only 6 free parameters, allowing 7 testable predictions. The values of V_us, V_cb, V_ub, m_u, m_d, m_s and m_b are then predicted as a function of the 3 charged lepton masses, m_c, m_t and tam β, the ratio of Higgs vacuum expectation values. In particular, the Cabibbo angle and m_s/m_d are determined in terms of only lepton masses. All predictions are in very good agreement with experiments