Gene-seed is used to upgrade your hero's tactics. Early in the game, you will not have enough gene-seed. Be judicious about which heroes you keep and level. As you progress, you will have more and more good heroes, and the heroes you roll will be less and less good by comparison. When you dismiss those heroes, you get extra gene-seed. So you will end up with more than enough gene-seed. Also, if you use maxed out heroes you will get LF but no corresponding XP, which means you'll have more LF for lesser rally, giving you more gene-seed.