Lugh’s comment on The Evil of Eugenics plot-a-day inspired me to write up a plot-a-day for Genetic Engineering. Lugh basically suggested that wizards created monsters in genetic experiments as a weapon against an undead horde, which is a nice and modern take on the origin of those creatures.

Genetic Engineering is really a staple of fiction by now. It usually goes horribly wrong, unleashing monsters or designer plagues on mankind. The sort of story you would associate with Genetic Engineering roots in Frankenstein and encompasses a lot of Post-Apocalyptic fiction; at the high end an unstoppable virus has become a popular alternative to global thermonuclear war for the purpose of destroying Earth to allow for such a setting or story.

Ignoring the total destruction of human society – which is usually a setting choice rather than a plot device – Genetic Engineering can be used in many ways in your adventures or stories.

• The evil villain is breeding an army of unstoppable mutants – usable in (almost) any campaign and setting. The player characters need to stop him from unleashing that army. Perhaps the villain is already using some of his creations to terrorize the nation or to assassinate politicians that stand in his way. Even the Aliens movie franchise could be seen as a variation of this idea (and indeed, Alien Resurrection picks up on that theme).
• Genetically engineered plants and creatures often feature in the colonization of other planets; realistically, Mars could be terraformed with their help. And you know what may happen next, of course – the plants used begin to mutate, the animals go crazy, and some may even develop intelligence. Depending on your setting this could result in anything from man-eating insects to a full exotic and alien ecosystem. Jungles on Mars! But that is setting. The players may have to investigate why colonists in an outlaying mining town disappear, and then find a way to exterminate the smart bugs, or they may even have to protect the new Martian ecosystems from an evil Colonial Authority that attempts to eradicate the “mistake”.
• A lone mutant runs rampant in a city, and the PCs have to stop him.
• Genetically-modified humans are patented and used as a slave labor force by an evil corporation.
• According to urban legend, Stalin wanted to breed  human-ape crossbreeds to be used as soldiers. While there seems to have been little to this, at least one Russian scientist was conducting experiments to that end. No matter what the purpose, such experiments pass as unethical by today’s standards, and the PCs might have to look into a scientist who is doing follow-up experiments of the same nature. Or it could lead to a Planet of the Apes scenario.
• In general, genetically-modified pets may go on a rampage.
• A corporation on a distant colony world / in a dystopian future controls the world’s grain because it genetically engineered it in such a way that it is not viable after the first generation. Each year, the farmers have to buy new grain from said corporation which is abusing this monopoly more and more. The antagonists need to step in and end this injustice once and for all.
• Genetic engineering is usually portrayed as “evil”, but it doesn’t need to be. A good, easy twist would be to offer a genetically engineered vaccine that is the only thing that can save mankind from a mutated plague; or a certain type of genetically modified grain that could solve a famine. If the producer of these is then less than clean – say, they also use their products for “evil” things – that sort of plot could offer a good amount of conflict of interests.
• To cover another cliche: It’s not people who are behind the genetic experiments, it’s aliens. This can easily become zany, too, if you combine it with any sort of whacky conspiracy theory. Then twist it around and set it in a High Fantasy world.

There are surely countless other ideas, but that’s what I can come up with for now.