The other universe which the wave passed through was very similar to ours except for one big difference: every human who had ever existed or ever would was the opposite sex to the sex they were in our own. So when it spread across the world, everybody would be transformed so that their sex was reversed.
Every male human would have his Y chromosome turned into a second X, and so his body would reshape to be more petite and lithe, curves would form from his flesh and his skin would turn more supple and smooth, his facial features would turn feminine, mammaries would form in his chest (and so every adult male would grow breasts), his penis would shrink away to a clitoris, his testicles would reform into ovaries and his scrotum would open out into a vagina (plus if he had impregnated a woman who was still carrying it, now she would become pregnant herself).
Every female human would have her second X chromosome turn into a Y, and so her body would firm up and grow taller, larger and more muscular, her shoulders would widen and her figure would turn more straight, her skin would roughen up and grow more hairy, her facial features would become masculine, her breasts (if she had them) would shrink away into her pectorals, her clitoris would lengthen and thicken into a penis, her vagina would seal up and her ovaries would move down into it and turn into testicles as it formed into his scrotum.
There were two big mental changes: first, everyone's sexuality would swap (unless they were bi or pan or the like). Straight people would be attracted to their old sex, and gay people to their new sex. And second, everyone who had a sex drive would have it amplified immediately following the change. They would want really hard to get to have sex with someone in their new bodies.