Sex roles in dance are a vexing question, and one that won't go away: dance is so closely tied to the body that you can't make a dance without somehow implying a point of view on the subject. Even the most studiously androgynous piece makes a statement, if only that there are no gender differences. The flashy, accessible River North Dance Company both relies on traditional sex roles (often derived from older dance forms) and offers new twists on them. In Frank Chaves's Thief, a dance for four couples, men and women alternately perform the same choreography--not surprisingly, with completely different effects. In Chaves's Passion, a woman is romanced by two men and chooses the gentler, more "feminine" one. And in Tony Savino's Swing Partners, the sexual energy spills all over the stage as men jitterbug with men, women with women, and men with women. The bottom line is that in the dance world sexuality is a fluid, shifting force as constant as a heartbeat. Sherry Zunker Dow's well-trained, hungry five-year-old troupe perform their clever, entertaining brand of dance extremely well. On this program they're offering all of the above, plus Zunker Dow's popular Reality of a Dreamer and her newer, more ethereal piece for seven women, Glimpse. Also on the program are Chaves's Fixe and Grandma's Hands, Harrison McEldowney's humorous Perfidia, and the company premiere of Sam Watson and Kenneth Comstock's Wired, a dance that on the many occasions I've seen it has never failed to elicit screams of laughter. Friday and Saturday at 8 at the Athenaeum Theatre, 2936 N. Southport; $18-$25. Call 902-1500 for tickets or 944-2888 for group-discount tickets.