A classic example of sexual selection is the peacock's tail. The long, elaborate tail feathers do nothing to promote survival of male peacocks, but they are very important in determining which males attract mates and which don't. If you'll recall, when we originally derived the Hardy-Weinberg principle we said that the matings occurred randomly.
Sexual selection is clearly an instance of non-random mating.
Let's go back to our original mating table and see how we need to modify it to accomodate sexual selection. What I've done is to assume that there is random mating in the populations among those individuals that are included in the mating pool . We'll assume that all females are mated so that . Then it's not too hard to convince yourself that where . And we could derive similar equations for and .