justify it. So you say that it's a result of genetic mutation caused by a Freak Lab Accident.
However, could that really work? Let's say you want this character to be able to fly. But without wings, where would the propulsion come from? Let's say you want this character to be able to grow 100 times their size. What about the law of conservation of matter? (Not to mention that even if it was possible, the person would probably die from insufficient amounts of blood.) Let's not even get started on creating fire out of thin air...
Many writers don't know (or deliberately ignore) that genes are only responsible for protein synthesis. This is when said writers give genes the ability to alter the very laws of physics (or other universal laws) — or at least the ability to do things that would be impossible for a human. In this case genes, instead of a component of cellular biology, might as well be magical talismans carried inside the body. LEGO Genetics is often involved as well. Extra fail points if the writer ignores the necessary secondary powers needed for the Functional Magic to actually be functional, such as Photographic Memory for Voluntary Shapeshifting etc.
If the writer wants to firm up the science, they might say that the genes merely construct nanoscale Applied Phlebotinum in your cells which acts on "quantum forces not yet discovered" or some other Hand Wave, but it's still really Functional Magic given a pseudoscience gloss-over.
Some types of superpowers being caused by genetics are plausible. Super-Strength could be from extra muscle mass or more efficient contractile cells (but you still won't be strong enough to bend girders bare-handed), low-level Super-Speed would be a snap as natural human neural impulses and reaction time are notoriously sluggish (slower than sound, in fact) and could easily be sped up by increasing conductivity, claws could be some sort of bone growth or modified keratin, and there are animals that use electricity as a weapon, can stretch and distort their bodies, or have a Healing Factor or Super-Senses. While you can't become an invisible man, chromatophores in the skin could give you super-camouflage. Etc.
Genetically-based Psychic Powers are automatically a subtrope of this, as are any Mage Species. Characters who are Randomly Gifted usually don't gain their powers from genetic sources, or in combination with other non-genetic factors.
- The Meta-gene of The DCU. A single gene that provides every possible super-power. Various Human Aliens like Superman, the Legion of Super-Heroes, Martian Manhunter, etc. also attribute their abilities to genetics — transfer their DNA into a human, and that human becomes super-powered.
- Certain villains in Spider-Man also have these kinds of abilities. Spider-Man himself sort of doesn't count as he "does what ever a spider can..."
- In Strontium Dog, Johnny's mother gets caught in a fallout shower while eight months pregnant with Johnny; as a result, Johnny's eyes mutate to be able to emit alpha particles, which gives him X-Ray Vision and limited telepathy. Not only is this biologically impossible, but alpha particles do not work that way! In fairness, however, Johnny is an exception; 99.9% of the other mutants are just disfigured, with the lucky ones getting extra body parts.
- Attempted to be justified in Ultimate Fantastic Four, at least with Mr. Fantastic and the Human Torch. Johnny's powers come from his nuclear fusion, using his body as an energy source. Reed is able to stretch and not crush his organs because all he has in the way of organs is a colony of symbiotic bacteria who take in food and air and give his body nutrition. Their origin is justified as well now too, as their powers are not from cosmic radiation anymore, but rather from swapping bodies with a double from another universe. They should just pray they'll never catch any disease that requires treatment with antibiotics...
- Wild Storm has Apollo from The Authority, genetically engineered to fly and fire solar blasts, the "gen-factor" of Gen¹³ and its spinoffs, and the WildC.A.T.S., who get their powers from alien DNA.
- Most mutants in X-Men such as Storm have the ability to use physically impossible powers as a result of their mutation. Sometimes they come from a mutation of a single gene. Justified in-universe via experimentation on proto-humanity by a race of sufficiently advanced aliens. Comparable to how freak lab accidents can give normal humans superpowers in the Marvel Universe, the infamous "x-factor"/"mutant gene" serves to makes the activation of these powers a natural part of the mutant's biology. The Galacta: Daughter of Galactus mini-series claims that the X-factor actually gives all mutants the same power: the ability to bend reality. None of them can consciously control this power, so it manifests in different ways, giving the appearance of different mutant powers.
- In Child of the Storm, there's an M-Gene and an X-Gene, for magic and mutant powers respectively, though more properly, they're genetic sequences rather than individual genes, making it marginally more plausible. As in Marvel Comics canon, they're derived from experimentation by the Celestials. They tend to run in families, as does the power level, though not invariably. Not only are there squibs, but Jean Grey, Maddie, and Harry, being second cousins (on Harry's mother's side and Jean's and Maddie's father's side), share vast Psychic Powers — though Jean and Maddie is significantly stronger than Harry. However, it's noted that while the Grey bloodline had a psychic or two every now and then, most of them were relatively weak, nothing compared to the latest generation. This is partly explained by the fact that they originally descended from a branch of the Clan Askani, which seemed to have lost its psychic spark... until recently.
- Rainbow Toes was a... rather wacky Outsiders fanfiction work from fanfiction.net that was removed and has vanished from the internet for several years now. The premise was there was a hereditary transformation from Ponyboy Curtis' paternal side of the family that made the men transform into literal clowns with genuine magical powers. While his father only sported rainbow-colored toenails and was capable of a few parlor tricks, Pony transformed into a full-blown clown complete with magic powers that gradually gave him control over reality itself. He adapted to it pretty quickly.
- Deryni powers are genetic ... mostly, and Katherine Kurtz made a real effort to make it sound realistic. There are basically three types of magic-users in the Deryni world:
- 'True' Deryniness is a dominant sex-linked trait: a single gene on the X chromosome controls access to Deryni powers, and eggs with the 'Deryni allele' are hardier and more fertile. Having this allele on one X chromosome is sufficient to make a person Deryni. Exactly which powers an individual Deryni has is determined in other ways — Healing powers, for example, are rare among Deryni, but they are definitely heritable.
- The Haldane royal line, and perhaps a few others, carries a different gene for Deryniness. This gene is also sex-linked: it's carried on the Y chromosome, making it exclusively male. A person with this gene can't learn Deryni magic; instead, he must undergo a specific empowerment ritual, after which he has immediate access to a specific and limited set of Deryni-like powers and abilities. In a milieu where God is very real and religious magic can do things that regular magic can't, there's an implication that this gene and the associated power are connected with the Divine Right of Kings.
- A few individuals have no known Deryni blood, nor are they Haldanes as far as anyone knows, but they do have the ability to wield magic. A good example of this is the mysterious Warin de Grey, who plays a major role in Deryni Checkmate and High Deryni.
- In the Gentleman Bastard series, magic is inherited but "does not breed true". Genetics is barely a thing, let alone understood, in the setting, but the implication is that there is a large number of genes with very different and interacting expression mechanisms involved. Mages take genealogy seriously, but bristle at the idea of being bred like cattle, and at the time of the story five of the hundreds of mages that have lived in the past centuries had parents who were both mages.
- J. K. Rowling has stated that there was a Magic Gene involved in wizarding capabilities in Harry Potter. This gene could also be present in other magical species. It can remain in a bloodline for generations before manifesting in muggleborns. The inverse is also the reason for squibs. This also doubles as Hollywood Genetics, since the gene is clearly defined as "dominant", but dominant genes cannot skip generations and squibs are much rarer than they should be. However since the gene itself is magic, it can presumably do whatever it likes.
- The Maximum Ride series have children who are "genetically engineered" to have wings. And occasionally other New Powers as the Plot Demands. Weirdly, it is implied that the early powers that they spontaneously develop were also engineered into them, to help them fulfill their purpose to "save the world" or whatever. In The Final Warning though, Jeb comments that they seemed to be randomly mutating and developing powers on their own, which first manifests with Nudge getting magnetic control.
- According to Word of God, Magyk in Septimus Heap has a genetic basis, which is why Princess Jenna has no Magykal powers, unlike her adopted siblings. Subverted when Jenna is made into a witch in Darke.
- Skulduggery Pleasant has magic running in families, to the extent at least one particular type from a particular set of ancestors apparently manifests 'in the blood' so to speak.
- Wild Cards, full stop. Apparently a virus containing psionic aliens' DNA can do anything. Technically a case of Applied Phlebotinum. The Ilkazam Enhancer (i.e. the Wild Card Virus) was biotechnology designed to bestow superhuman powers. Sometimes it even worked.
- Bewitched seems to have this. Witches and warlocks are only born to other witches and warlocks, and Tabitha has strong powers, while Adam has powers, although weak.
- Nowhere on television is this trope in effect more than Heroes. Apparently everyone's powers, from regeneration and invisibility, to clairvoyance and time travel, are just a matter of having the right DNA.
- All powers in Mutant X come from genetic experiments conducted by Genomex and the Dominion. These powers include generating electricity, density manipulation, throwing energy balls, time travel, etc.
- Ditto for Painkiller Jane. Yes, time travel included. Especially ridiculous since all Neuros are rejected immortality experiments.
- Stargate SG-1 has a Goa'uld Mad Scientist mutating humans to give them Psychic Powers in order to create a super-host.
- Star Trek: The Original Series: Mr. Spock's ability to mind-meld comes from his Vulcan genes.
- GURPS Bio-Tech has a section on magical genetic engineering. Along with replicating scientific possibilities, it allows genengineering ability to cast any spell into a not-yet-born child. It is cheaper than making an ordinary magical item, but risks making a Phlebotinum Rebel. Otherwise, it tries hard to avert this trope. For example, angel-like wings can be genengineered, but don't give ability to fly in 1 G. They might be useful at lower gravity or in a space habitat, though.
- BioShock is made of this trope: The game establishes that in-game Plasmids and Gene Tonics work by rewriting their user's genetic code from scratch to allow for fantastic new skills...such as being able to summon fire, lightning, and worst of all, bees from your hands.
- Mass Effect:
- Averted with the gene therapy that is standard issue for soldiers and provided free for citizens by most governments, resulting in widespread perfect vision and hearing, robust immune systems, and a near elimination of genetic disorders in industrialized areas. Only modest physical enhancements are available, however, with 8%-12% increases in adrenal response, clotting speed, and muscle retention etc. considered state of the art.
- Played with in Mass Effect: Andromeda with the Kett. Their use of genetic engineering is so advanced that they have the technology to make a lifeform transform into a different lifeform in less than a minute. In fact, this is how they reproduce. However, the fact that their genetic technology is commented on in-universe to be shocking implies that their genetic engineering technology is a case of sufficiently advanced technology, thus explaining the lack of realism.
- A recurring theme in Star Ocean: Till the End of Time.
- Two words: Symbological Genetics. Tinkering with genes can give you magic powers.
- Star Ocean: The Climax Boss and Final Boss were created through genetic engineering to survive a Mordor planet. There is also a species that naturally possesses magical genetics.
- Star Ocean: The Second Story: The main villains were a group of people who were granted god-like powers above the normal magic available to their species in order to take over the universe.
- Star Ocean: The Last Hope: Following World War III, three human babies were modified to survive in harsh and irradiated environments, and gained magical powers in the process. The DNA used to do this was taken from a human subspecies that also had magical genetics naturally.
- Deconstructed in Tabula Rasa. All player characters are Receptives, or people who have the right sort of genes to allow them to use Logos. However, this is only because those genes are the correct "password" to access Logos Shrines left by the Eloh and receive Logos Element information from them. It's essentially a security system the Eloh set up thousands of years ago by modifying some early humans to express those genes. What's more, several quests in the game revealed that the AFS was conducting research into providing non-Receptives the same ability to use Logos. Volunteers met horrific ends, such as fast-growing terminal cancers.
- RWBY: Faunus genetics are mentioned to be a pain for scientists to understand. Each Faunus has a single animal trait from a specific animal (such as cat ears or a monkey tail), but these traits seem random; one cat Faunus might have cat ears, while the other could have a cat's tail. If two Faunus of the same animal species have a child, the child will be the same species, but if two Faunus of different animal species have a child, the child will be a completely random species. If a human and a Faunus have a child it's even odds whether the child will be a Faunus of the same species as the parent or human. It's also mentioned it can sometimes take time for Faunus traits to manifest.
- Reasonably justified in Homestuck:
- The main characters aren't genetically related to humanity at all, and their DNA presumably could differ drastically from normal DNA in order to allow their powers. Trolls however play a little looser with DNA and there's at least one distinct sub-species of Troll, so there seems to be wider genetic variability to begin with for them. However, two of the players were born naturally for their species and were never even meant to play the game but still get the powers of their assigned class so the powers may not have a genetic origin.
- The brings known as First Guardians are genetically engineered using DNA codes from the dreams of the players, although the energy source for their powers is the Green Sun. This makes even less sense with Doc Scratch, who was created this way, but he is a puppet with a cue ball for a head and so shouldn't even have DNA.
- Spinnerette develops a Deconstruction. Spinny and her other supra-humans have special genes thanks to lab accidents and mutations, but (since many are scientists themselves) readily admit that genetics is insufficient to explain their incredible physics-defying powers. Instead, their genes allow the Cherenkov-Kirby reaction to occur within their bodies, giving them access to theoretically unlimited energy. C-K radiation is effectively the setting's Applied Phlebotinum, and its connection to genetics is not clearly understood.
- Mutants in the Whateley Universe have genetic changes in a host of different genes, labeled the 'meta gene complex', and gain the ability to use some sort of extra-dimensional energy that's supposed to be the power source for the various impossible powers.
- In Danny Phantom, the titular character gained his abilities to become a ghost and use ghost powers after the ghost portal mutated his DNA, combining it with "ectoplasm".
- In Street Sharks, somehow using a formula and the blood of Genghis Khan turns a lobster and a marlin into huge evil mutant soldiers. Injecting the formula and animal DNA into a human turns them into non-evil mutants which are twice the size of their human forms, very top heavy, and able to eat virtually everything (including metal). This one got to fly under Rule of Cool because the Street Sharks were totally jawsome.