It's known that a cross between two specific strains of watermelon will result in the production of seed, that when grown result in the production of a seedless watermelon.

So, if you know exactly which strains are used to make this cross, or the genetic mechanics that result in an F1 hybrid that is sterile, would it not be possible to grow one plant of each, hand-pollinate them, and end up with lots and lots of "seedless watermelon seeds" that can be grown the following year?

I realize there are often patents in place that make it illegal to do some things, but this is more along the lines of a hypothetical situation. I'm guessing it "should" work, right?

I suppose another example would be, say you personally made a cross that resulted in a fantastic plant, but some disaster struck and you lost your plants/seeds. Couldn't you just duplicate the cross to get the same hybrid you previously lost?

Thanks for any insight or personal experience in this sort of thing.

Yes.

I suppose another example would be, say you personally made a cross that resulted in a fantastic plant, but some disaster struck and you lost your plants/seeds. Couldn't you just duplicate the cross to get the same hybrid you previously lost?

Yes sometimes and no sometimes. You can only get the same hybrid if its parents are inbred lines or the equivalent (for example two normally self-pollinated varieties of a crop that have been specifically cross-pollinated to produce the hybrid). If the plants that have been crossed are from a normally cross-pollinated plant species then the seedlings will most likely all be different each time the cross is made.