Gene Hunting

The protagonist has been happily living with his or her family until one day, out of the blue, they learn that the people who raised them are not in fact their biological 'rents, either by adoption or by infidelity. There begins the gene hunt, to find their genetic parents. Expect lots of Freudian Excuses, You're Not My Father and "are my adoptive parents my real parents" Wangst. Often the result of Parental Abandonment or Raised by Wolves.

There are a few different ways this can play out: firstly, they find their genetic parents and discover happiness (this only works if the old parents are distant or abusive). Secondly, they can find their genetic parents, only to find they are more distant or jerky than their adoptive ones (expect lots of Prodigal Son-style making up at the end). Thirdly, they can locate their biological parents, only to realize that they'd rather not confront them and risk disrupting everyone's lives. Finally, they can fail altogether to find their parents (a real Downer Ending will have the character give up just before they would have found their parents).

Can lead to Luke, I Am Your Father, Luke, You Are My Father, Family Relationship Switcheroo, Tell Me About My Father, or Mysterious Parent situations. If this happens in a Sitcom, be wary when Status Quo Is God. Named for, but unrelated to, the character of Gene Hunt on Life On Mars.

Should not be confused with Stalker with a Test Tube, an entirely different form of gene hunting. When handled poorly, this can carry a great deal of Unfortunate Implications in regards to relationships between adopted children and the parents who raised them (ie, no blood relation = no love/not family).

Not to be confused with Gene Hunting

Examples of Gene Hunting include:

Comic Books

DC Comics: Damage. Thanks to genetic engineering, he was genetically the child of the entire JSA. His birth father was the Atom (Al Pratt).
This is the backstory of Izzy Sinclair, from the Doctor Who Magazine comic. In the end, she doesn't find her birth parents, but she does reconcile with her adoptive parents (making this a Type 3 with a happy ending).

Fan Works

A common premise for Pan's Labyrinth fanfic.

Film

The Ben Stiller film Flirting With Disaster.
The entire premise of Joe Dirt, minus the part where he was adopted. Result: They're jackasses.
The title character in Astrid Lindgren's Mio my Mio.
The driving plot of the movie Twins has the main character leaving his island to search for his family, finding a brother, maybe a father, and finally a mother in the process.
Secrets And Lies is all about somebody looking for her birth mother, though she knew she was adopted all along, the death of her adoptive mother triggers the search.

Literature

Flinx and his search for his genetic father in Alan Dean Foster's Humanx Commonwealth book series. It's played for quite a bit of Wangst and at least two Are You My Father moments, before being concluded in a fairly brutal fashion in the penultimate book, when he discovers that he doesn't technically have one thanks to the wonders of genetic engineering.
Taran's search for his father in Taran Wanderer, the penultimate book of The Chronicles of Prydain by Lloyd Alexander. He never finds out, and realizes that it's not that important anyway.
Lyra Belacqua in His Dark Materials was always told that her parents were the Count and Countess Belacqua, who had died in an airship accident; she later discovers that they were actually her aunt and uncle, and her real parents are (this is despoilered halfway through the first book) Lord Asriel and Marisa Coulter. Lyra reacts both ways to the news: while her mother's identity comes as a nasty shock, she couldn't be happier to learn of her father and delights in hearing how he murdered her mother's legal spouse when Lyra was a newborn.
The young adult novel The Girl on the Milk Carton is about a teen girl that sees a picture of a missing girl on her milk carton and realizes it's her. She spends the rest of the book wrestling with the knowledge that her parents aren't her true parents, that she might have even been kidnapped by them, and that she has another set of parents that are looking for her desperately.
Inverted in Fingersmith: Mrs. Sucksby tries to exchange her adoptive daughter for her biological daughter who's been raised by a rich family (she thinks the girl will love her just by virtue of being her biological daughter—she's wrong).

Live-Action TV

Claire Bennet from Heroes. Eventually she finds her biological parents, and her dad turns out to a be congressman and Aloof Big Brother to the man who saved her life: Nathan Petrelli, destined to become President. Nice.
Rather amusingly done in Curb Your Enthusiasm, where Larry finds his apparent birth parents who are Christian (he is Jewish). After getting over the initial shock, he decides that he likes them, and consequentially loses all of his stereotypically "Jewish" tendencies (as well as becoming a nice nice person). After he finds out that they weren't his parents, and the people who raised him were, he reverts back to his old personality.
Somewhat subverted on Veronica Mars: after it's hinted that Veronica may not be Keith's child, she gets DNA results and then discards them without reading. Her father also got DNA results, but read his. Congratulations, V, your dad's still your dad!

Keith: You think that charm of yours is learned behaviour? That's genetics, baby!

- Also done with Trina Echolls. The degree to how well that ended is up for debate.
Chuck does this in season 2 of Pushing Daisies. Inverted with Emerson Codd, who tries to publish a book to lead his lost daughter to him.
"Are you my mummy? Are you my mummy?" Of course. It's not quite clear why this little boy is looking for his mummy, but the gene hunting does save humanity from zombification.
- Given the onscreen explanation of why the little boy was zombified by the nanogenes, it seems pretty clear that he was looking for his Mummy because that is what the little boy was doing when he was hit by the bomb.
Family Ties: In one episode Alex's friend Skippy goes through this, and is hurt when he goes to meet his birth mother and discovers she doesn't want to have a relationship. Alex finally says, essentially, "Look, the people who changed your diapers and have raised you all this time? Those are your real parents," and Skippy decides he's right.
One episode of Dharma and Greg has an old friend of Dharma visit and spend a lot of time with Larry. It turns out that the friend has determined Larry may be her biological father, and though she doesn't want to bring this up and disrupt his life she wants to bond with him just in case. Dharma eventually discovers proof that Larry couldn't be the father, but chooses not to reveal it when the friend says Larry was her favorite out of all the potential candidates.
The Korean Drama Winter Sonata: Joon Sang is a high schooler checking school records for who his father might be.
On True Blood Sam was adopted and then abandoned when his adoptive family found out that he was a shapeshifter. When he finds his biological parents and his younger brother Tommy, they turn out to be trailer trash who support themselves by having Tommy shapeshift into a dog and fight in illegal dogfights. When his parents abuse his hospitality he throws them out and wants nothing to do with them. He tries to build a relationship with Tommy but the kid is so messed up things quickly take a dark turn.
On Boy Meets World, Shawn gets a letter from his Missing Mom in which she reveals that she is not his real mother. He proceeds to try to track his real mother, and is unsucessful in doing so. His dead father later appears to him in a vision and says that his biological mom was a stripper who took off after giving birth to him, though it's unclear if this vision was real or all in Shawn's head.
In an early episode of Highlander the Series, orphaned Richie Ryan does this, to no success—the man claiming to be his father is a con man, and the woman he'd always believed to be his birth mother turned out to have been fostering him. This turns out to be foreshadowing, as Richie is later revealed to be an Immortal, all of whom are foundlings.
Gilmore Girls has a girl come into Luke's diner saying that she's doing a DNA test for her sicence fair to find out who her father is.
On CSI New York, the son Mac's late wife gave up for adoption as a teenager comes searching for her, only to learn that she'd died on 9/11. Although his Gene Hunting was a failure, Mac sympathizes with his could-have-been-stepson, and strikes up a friendship to tell him about his late mother.
Chico and The Man has a Japanese young man come and claim Ed Brown as his father, stemming from a tryst after WW 2, and how he elaborates on how he and his mother plan to move to LA to spend their lives with him. Turns out Ed's not the bio-father, it had been an Army buddy of his. Chico saves the day by falsely claiming that Ed's also his father and had been caring for him as well, letting the Japanese decide it's wiser for them to go back to Japan.

Newspaper Comics

The title character from British anthology comic strip Fishboy (yes, I kid you not, he was raised by fish) spends most of his time swimming the Earth searching for his parents and helping people along the way. He didn't find them before the strip was canceled.

Theatre

Mamma Mia!: Sophie, who has lived fatherless her whole life, finds an old journal of her mother's detailing three lovers she had around the time of Sophie's conception. So she invites the three men over, and instantly develops a rapport with one of them. Which one is her father? No one ever knows.
- The creators have stated that Bill is the father.

Video Games

Inverted, somewhat, in Final Fantasy IV: Orphan hero Cecil knows he's adopted, after a fashion, but his concern about his real parents is quite low-key. However, though he's not hunting genes, the genes are hunting him.

Web Original

Zigzagged in season 2 of Stationery Voyagers.
- Would have been inverted, since Neone's biological parents were interested in knowing what happened to her first.
  - But the inversion is subverted in that they were originally fully content to leave Neone to her ignorance to protect her from Intimidator Irendus.
  - However, they decided to make peace with their past and meet her anyway; since Friar Rubberion had confirmed Neone was Neotondo and Jante's daughter through a paternity test and wanted them to face their fears.
  - Then, Neone double subvert-inverts the subverted inversion by actively seeking to meet with them only to end the tabloid buzz, and not because she's terribly interested in being a part of a royal family. Does your head hurt yet?

Western Animation

The Simpsons episode "Homer's Paternity Coot", where Homer tries to track down a man who he suspects of being his real father.
Family Guy: Peter goes to Ireland to find his real father.
- And when Stewie hunts down someone he believes to be his real father who turns out to be himself.
Fran was adopted by a Chinese couple in American Dad. After Stan gets annoyed by their lack of assimilation, insistence on tradition, and refusal to treat him as "the man of the house" in his own home (they were pretty obnoxious and rude to him), he goes on a search for her real parents who turn out to be a pair of Complete Monsters (they gave up their baby rather than downgrade to Coach seats on a flight).
Rocko's Modern Life once parodied this in the episode where Heifer found out he was adopted. To clarify, Heifer is a steer who was literally raised by wolves. Ultimately, Heifer has a dream where his father informs him that he was abandoned at birth for being too much of a sissy. And that his mother's a car seat somewhere.
CatDog went looking for their parents, and believed they found their relatives in a little town in the mountains where cats and dogs get along. They're wrong, and also discover that the peace between cats and dogs is apparently really, really fragile. They eventually find out their real parents were (if I recall correctly, since the CatDog page doesn't say) a female yeti and a fish. Considering this probably isn't the strangest thing they've ever seen, they're very accepting.
- He is a frog with a very long nose, not a fish.
- They weren't even their biological parents. They were found outside their cave as babies and they took them in. Cat and dog are annoyed that they still don't know where they came from, but they knew who cared for them when they were young and that was good enough for them.
Moses in the movie The Prince of Egypt is shocked to find out he's not really a prince, but a Jew.
- He knew full well where he came from in The Bible. He murdered an Egyptian out of ethnic/nationalistic pride due to not wanting to see his own attacked by an Egyptian wrongly. The Prince of Egypt merely tidies the story up for young viewers, by making that whole murder thing an accident. The idea that he didn't know who he was actually comes from the film The Ten Commandments.
Po's arc in Kung Fu Panda 2 is driven in part by this, especially since he has faint memories of his original parents abandoning him. But he eventually comes to terms with both the fact that they loved him so much they died for him, and that his adoptive father loves him no less. Cue Crowning Moment of Heartwarming marathon.
Leela's personal plot in early Futurama episodes is this, though played with. As she belives she's an alien, she's looking for her entire race, not just her parents, and she doesn't have adoptive parents, she was raised in the orphanarim from childhood. She belives she finds the only other cyclops, but he turns out to be a shape shifting alien who only wants her to take care of one of his castles. She eventually discovers that she's not an alien, but a sewer mutant who looks mostly normal. Her parents left her on the orphanarium's doorstep because they wanted her to have a normal life and watched over her from the shadows her entire life. She vists them often in later episodes and tries to go back and have a life with them after being returned to a teen, but returns to normal.
Featured in the My Little Pony Friendship Is Magic episode "Dragon Quest", when Spike starts questioning his self-identity as a baby dragon raised by ponies. When Twilight Sparkle's research fails to yield any information, he joins the Great Dragon Migration to learn more about his species.