The 11th edition rules are intentionally written to be neutral on the issue. Specifics as to the genders of players and gender ratios of teams is determined by the event organizer and any rules concerning those are in addition to or in place of the standard UPA rules. The Mixed division of the UPA Championship Series uses 4:3/3:4 offense dictates.
Other events (tournaments, leagues, pickup, etc) may vary those ratios as their organizers see fit.