Complex sentence: The distribution of the members of the board tend to coincide with the political composition of the current Congress, with a "Concertación" (the government coalition) majority and an "Alianza" (right-wing opposition alliance) minority.
Split into simpler sentences: The distribution of the members of the board tend to coincide with the political composition of the current Congress. That is to say, with a "Concertación" (the government coalition) majority and an "Alianza" (right-wing opposition alliance) minority.