The generation of software architecture using genetic algorithms is studied with architectural styles and patterns as mutations. The main input for the genetic algorithm is a rudimentary architecture representing the functional decomposition of the system, obtained as a refinement of use cases. Using a fitness function tuned for desired weights of simplicity, efficiency and modifiability, the technique produces a proposal for the software architecture of the target system, with applications of architectural styles and patterns. The quality of the produced architectures is studied empirically by comparing these architectures with the ones produced by undergraduate students.