The Gracchi were not patricians. The gens Sempronia was a plebeian noble family and only became patrician during Augustus' promotion of several plebeian senatorial families to patrician rank, in order to preserve the order (which was really only distinguished by the ability to hold certain priesthoods). Clodius' gens Claudia was one of the few patrician families with surviving lines in 58--the nobiles of the late Republic were almost all plebeian