  We use results of M. Aprodu and E. Sernesi to extend a result by
Fulton--Harris--Lazarsfeld in Brill--Noether theory of line bundles %and, as
well, a result by Aprod-Sernesi in theory of Secant Loci,
  to Brill--Noether loci of stable bundles inside the moduli space of rank two
stable vector bundles on a smooth projective algebraic curve. As a consequence;
if $B^k_{2, d}$ is of expected dimension, then we prove that its smoothness is
equivalent with the smoothness of $B^{k}_{2, d+1}$.
