  Let $M(\gl)$ be a Verma module for a basic classical simple Lie superalgebra
$\fg \neq G(3)$ defined using the distinguished Borel subalgebra, and let $\gc$
be an isotropic positive root of $\fg.$ As a special case of our first main
result we show that if $\mu, \gl \in \fh^*$ with $\gl-\mu = \gc$ we have $$\dim
\Hom_{\sfg}(M(\mu),M(\gl))\le 1.$$
  This result applies to the construction of \v{S}apovalov elements for
isotropic roots. The proof rests on a comparison with the corresponding result
for a certain simple Lie algebra $G$.
