  A topological approach to quark fractional charges, based on charge
constraints unexplained by the Standard Model of particle physics, is
discussed. Charge fractionalization is related to a tunneling process occurring
in time between pure gauge field configurations at the far past and future
associated with integer-charged bare quarks, named prequarks. This transition
conforms to a topologically nontrivial configuration of the weak gauge fields
in Euclidean space-time. In this context, an electroweak $Z_{2}$ symmetry
between bare quarks and leptons, named presymmetry, is revealed. It is shown
that an effective topological charge equal to the ratio between baryon number
and the number of fermion generations may be associated with baryonic matter.
The observed conservation of baryon number is then connected with the
conservation of this charge on quarks. Similar results are obtained for leptons
in the dual scenario with local quark charges.
