Aaron,
Agreed that genes express a wide base of traits - either in dominant or
double recessive combinations.

This then leads on to another point of detail.

Taking that A.m.m. and other A.m. bees have not come into contact with
V.j. until man intervened - why should A.m. have the genetic blueprint
for SMR ready and waiting to be used?

Taking  antibodies in the immunity system as an example, the mechanisms
for producing the right proteins are there but the actual antibodies are
not, that is, not until contact has been established with the foreign
material.
Would it not be the same regarding the D.N.A sequence for gene code
protecting against Varroa.
i.e. the mechanism is there (mutation) but not the actual code ready and
waiting.
Unless A.m. has ALREADY been in contact in the past directly or
indirectly via an earlier bee type that has passed on its genetic
configuration.

Peter