Most mutations appear to be base-pair substitutions or base-pair
insertions. I do not know if there is data on multiple mutations at the
same time. I do remember some discussion of doubling.
I found a reference to a change that involves gross reorganization of the
genetic material: 1) Inversion 2) deletion, reciprocal translocation and
fusion.
There is no predictability of a random process btw.
JQ: If the new gene was fixed in the genome what protects this new gene
from
the same mutations that got it there?
Nothing, other than if the mutation has a selective advantage organisms
with the mutation might have an advantage over those without the mutation.
But the chances of a reversal of a mutation are quite small.