  We evaluate the finite 1-loop threshold corrections, proportional to
$tan\beta$, to the down quark mass matrix. These result in corrections to down
quark masses and to Cabibbo-Kobayashi-Maskawa [CKM] matrix elements. The
corrections to CKM matrix elements are the novel feature of this paper. For
grand unified theories with large $\tan\beta$ these corrections may
significantly alter the low energy predictions of four of the CKM matrix
elements and the Jarlskog parameter J, a measure of CP violation. The angles
$\alpha,\: \beta$ and $\gamma$ of the unitarity triangle and the ratio
$|{V_{ub} \over V_{cb}}|$, however, are not corrected to this order. We also
discuss these corrections in the light of recent models for fermion masses.
Here the corrections may be useful in selecting among the various models.
Moreover, if one model fits the data, it will only do so for a particular range
of SUSY parameters.

High Energy Physics - Phenomenology