Once in Hollywood, the contestants perform individually or in groups in a series of rounds. Until season ten, there were usually three rounds of eliminations in Hollywood. In the first round the contestants emerged in groups but performed individually. For the next round, the contestants put themselves in small groups and perform a song together. In the final round, the contestants perform solo with a song of their choice a cappella or accompanied by a band‍—‌depending on the season. In seasons two and three, contestants were also asked to write original lyrics or melody in an additional round after the first round. In season seven, the group round was eliminated and contestants may, after a first solo performance and on judges approval, skip a second solo round and move directly to the final Hollywood round. In season twelve, the executive producers split up the females and males and chose the members to form the groups in the group round.
In which season were contestants separated by gender to form groups?
twelve