Although
genetic
isolation
is
reduced
by sexual
or
parasexual recombination
or
by
special
mechanisms
of
recombination,
it
is
difficult
to
assess
the
effect
of
these
recombination
processes
since
in
nature,
the
frequencies
with
which
they
occur
are
unknown.
In
bacteria,
the
problem
is
further
complicated
by
the
presence
of
extrachromosomal
pigments
which
initiate
chromosomal
transfer
and
rearrangements.
Nonetheless,
when
many
strains
of
a
given
microbial
group
are
analyzed,
it
is
possible
to
divide
them
in
a
series
of
discontinuous
groups
and
such
groups
can
be
recognized
as
species.
| 
