FYI, you can isolate the males away to extract the pollen, and even store it for later use. You can then carefully brush it on just some of the buds on a female, so they are the only areas that seed out. You basically could still get your whole crop, plus a few seeds that way, if you wanted too.
Also, you can take a cutting way early on (make sure to label the cutting and host plant), just like the one you got in the cup of water, and put it directly to 12/12 lighting in a different spot.. Like a cupboard or something with a small cfl.
The clone will sometimes show sex before it even roots out, usually within a few weeks. That way, you can keep vegging the main plant, and also know sooner than later if you should cull it or not, without waiting around to find out, and wasting resources and space on males. Handy trick that helps in different situations, when your starting out, etc..