Two-species couples open up a lot of questions about what their children will look like. This is avoided in many cases by having all boys look like their fathers and all girls look like their mothers. This can also apply to different types within the same species
(e.g., in Lady and the Tramp, the eponymous dogs are of different breeds. Female offspring look like their mother, the one male like his father).
In American media, female dogs are often represented by poodles, and occasionally other elegant-looking breeds like Malteses, Salukis, or Bichons; other breeds, and mutts, are usually male. Also, almost all cats are female.
It should be noted in male/female same-species examples given here that it is possible for traits to be sex linked. Since human females have two X chromosomes and males have one X and one Y (usually; there are cases where it is not so clear), diseases or other things can be restricted to one sex. One example is colorblindness, about 5.8 percent of males, but less than 1 percent of females, are colorblind in some way or another (although it should be noted that males get their X chromosome from their mother, so whether one's father is colorblind has no influence on whether one is colorblind himself).
This can be even more true with some insect species that have fewer chromosomes to worry about. At least one species of ants actually has the genetic material of the two sexes completely separate.
Compare with Bizarre Sexual Dimorphism, where a single species has very different-looking genders, and Patchwork Kids, where the children look (and often act) like a perfect mix of the parents. (Of course, with Tertiary Sexual Characteristics it's quite reasonable that these would be- and are- passed on from same-sex parent to child...)
You can expect this trope even more when at least one of the parents is a member of a One-Gender Race.
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In the Burger King commercials, The Burger King has a human wife, a human daughter, and a son with a freakish plastic head like his own.
The Whopper family, who consist of: Whopper, Mrs. Whopper (who is human), Whopper Jr. (which would make Whopper's full name "Whopper Whopper Sr."), Spicy Whopper, and teen-aged girl (who is also human). God help that girl, if they invent the Whopperette.
Since the late '90s, Jack In The Box commercials have featured the eponymous "Jack" who has a ping pong ball head. In later commercials, his blonde normal-noggined wife Cricket was introduced. However their son Jack Jr. has the same gender-specific head defect as his father. Jack's own father was also shown to have the ping pong ball head. His (normal head-ed) mother even asks him: "Have I ever told you how difficult your birth was?" Similarly, Jack's brother (seen in prison once, and then at a family photo) has one of the large heads. To make matters the more confusing, "Grandma Box" gave them the long-pointed nose (as she has a normal head but a long nose). We also recently were introduced to his cousin from Philly who has the same ping-pong head with a mullet. He too has a normal human wife.
The adverts for the Silentnight range of beds and mattresses feature a cartoon family consisting of a Hippo father and a Duck mother (who is much smaller than her husband) with a duck daughter and a (large) hippo son. Just think about that for a while (or rather, don't).
Inverted in an unusual case in Trigun with the Nebraska Family. It's unusual in that the two species in question are not animals, but human and giant: the human father and giantess mother have a normally-proportioned human daughter and several giant sons.
In the ending of Fullmetal Alchemist, Ed's son retains the Xerxesian racial traits of his father and grandfather, while his daughter is an ordinary Caucasian girl like her mother.
The above picture is from a Hentai manga story, My Younger Sister Is a Scylla, where a Scylla baby (human top half with octopus tentacles instead of legs) is adopted by a human fishermen family and marries her stepbrother once adult.
This is the case of Hiei and Yukina in YuYu Hakusho, as Yukina is an Koorime, like their mother, while Hiei is a fire demon, like his unseen father
In One Piece, when fishmen and merfolk have children, the child will either be a pure fishman or a pure merman/mermaid, not a hybrid, due to the special genetics of their breed which means that the children don't get their genes from their parents, but instead from one of their ancestors. Incidentally, it seems that are many more fishmen than fishwomen and many more mermaids than mermen.
Subtly utilized in Usagi Yojimbo (all previous pairings being same-species), when Ino (a pig) and his wife (a... round-eared animal) are later shown with their daughter, a round-eared animal like her mother. According to Word of God, it always works like that — women are always the same kind of animal as their mothers, and men as their fathers.
This is the way Sonic and Sally's children are represented in all of the flashforwards in the Sonic the Hedgehog comic. The recent "30 Years Later" storyline shows this to also be true for Tails and Mina's children. This also applies to Bunnie and Antoine's children, though Depending on the Artist, the boy may have Bunnie's coloration and the girl Antoine's. Somehow, they both inherited robotic limbs from their mother. A notable exception is Jon, the son of Rob O'Hedge and Mari-An. Despite being male, he is an Echidna like his mom.
Used in the third issue of the Spanish-for-a-French-market comic Blacksad. The chief of police is characterized as a German Shepherd, his wife is some sort of spaniel. Their son is also a German Shepherd, and their daughter the same spaniel breed as her mother.
Averted in the underground comic of "Dino-Boy". He's a human with a dinosaur body (or a dinosaur with a human head) who married a human woman. Their kids are both half-dinosaurs — but the son has a human body and a dinosaur's head, while the daughter is like her father.
Averted in Fables with Snow White and Bigby's kids; before they learn how to change shape, both boys and girls cover the spectrum from fully human-looking to human-wolf to fully wolf-looking, and one, well... takes after his grandfather.
Averted in the sequels to Balto, where the eponymous wolf/dog hybrid's litter with his red-furred husky Love Interest Jenna all take after her, except for his youngest daughter Aleu, who looks even more like a wolf than he does.
All of the red puppies look like Jenna in general but two of them look different from the others. One, Dingo, has a red stripe connecting to his nose and another unnamed puppy has a face that is entirely red except for their muzzle.
At the end of Lady and the Tramp, their puppies are three pure-bred cockers like Lady, and the boy Scamp who looks just as much a lovable mongrel as his father. They should ALL be mongrels to one degree or another.
The animated film Rover Dangerfield appears to have the "breeds" version of this, Daisy (a collie) has a litter to Rover (a basset hound) and produces several apparently male basset hounds and one possibly female collie.
In the 3rd sequel of Open Season, married couple Elliot and Giselle end up with two baby does and one buck, with the does looking exactly like their mother (only difference being the color of noses - red and black), and their son the exact copy of his father.
Films — Live-Action
The Szalinski family in Honey, I Shrunk the Kids. Amy has Diane's blonde hair, and Nick is a brunette who wears glasses just like Wayne is. Averted in Honey, I Blew Up the Kid, where Adam resembles his mother.
In Mom and Dad Save the World, the planet Spengo has two humanoid sentient (?!) species, one of which resembles humans. The other consists of males that resemble bulldogs and females which resemble carp.
In Northern Lights, witches are an all-female species that mate with human males. Female offspring are witches, male offspring are human.
Of a sort: though background Marat characters are of both genders, all named characters of any tribe are the same gender. All named members of Gargant, Wolf and Herdbane tribe are male, all named members of Horse tribe are female. There are no named members of Fox tribe, which was killed in its entirety before the start of the series, but the only Fox character discussed and described was female.
In the same series, it's remarked that up until now, nobody had ever seen a female Cane (giant wolf person), leading to rumors that there just weren't any.
In Piers Anthony's Xanth novels, fauns and nymphs are males and females of the same species.
This concept is parodied and then subverted in Scrubs when the Almighty Janitor fantasizes about being married to Elliot. They are surrounded by little girls dressed as doctors like Elliot and little boys dressed as janitors like The Janitor. Elliot wonders if they're "pigeonholing the children," and The Janitor points out that it doesn't matter because they aren't their kids.
Subverted In Bewitched: the protagonists are a witch and her non-magical husband. Their daughter has magic powers, while their son at first does not seem to have powers. It turns out he does, but he just didn't use them because his father does not like for them to use their powers.
Centaurs on Xena: Warrior Princess are an exclusively male race, they mate with human females and if offspring are male, they are always centaur, female children are always human.
The Eberron campaign setting uses this to escape having to make stats for half-Kalashtar. Justified by the spirits which define a Kalashtar bloodline having clearly defined genders.
In the Tormenta setting, minotaurs are a playable race with their own nation inspired on Rome. There are no female minotaurs. They mate with humans (generally their slaves) or Half-Elves, and the males are minotaurs, while the females are from their mother's race.
This was true of AD&D 2nd edition in general for One-Gender Fey Races like satyrs, nymphs, sylphs or dryads.
In the systemless Zodiacs campaign guide, it is mentioned that any child has roughly a 3 in 4 chance of being the same species as their mother.
Pokémon averts this. The child of two different Pokémon will always be the same species as the mother, regardless of the father. Although if either parent is Ditto, the child will be the non-Ditto parent. For male-only species, such as Tauros and Hitmontop, they can only reproduce their own species by breeding with Ditto. This is justified, as all Pokémon species draw from the same gene pool, and are actually subspecies.
Played straight with certain Pokémon whose genders are so different that they are classified separately, but the above rules still apply when crossbreeding (e.g. the child of a female Nidoran will be a Nidoran of either gender, but the child of a male will be whatever species the mother is.) See also: Hot Skitty-on-Wailord Action.
Lampshaded in Knights of the Old Republic 2, with a Human sub-species or variant species that specifically works this way, the Echani. The somewhat creepy Echani Handmaidens all look identical because Echani always physically take after the parent of the same gender. The one exception is a pariah because the fact that she looks different is a sign of their father's infidelity — and because she looks exactly identical to her mother at her age. The creepiness is enhanced by the credible fan theory that the Handmaiden's mother is Kreia.
Chibi-Robo extends this trope to Living Toys. The son of Mort and Princess Pitts is a mummy action figure (like Mort), the daughter is a princess doll like Pitts.
Averted elsewhere in PoR and RD however — notably, the child of a beorc and a laguz will not follow the species of either parent. They will instead have a human body, with heightened powers and longevity from their laguz blood. For a more specific example Soren's looks trend much more toward his mother than his father, but he resembles neither closely enough to be identified as their child on sight, although he bears a reasonable resemblance to his uncle in hindsight.
In Genealogy of the Holy War, the class of the Second Generation girls is determined by their mother's class: Lakche is a Swordfighter, just like Ayra; Fee is a Pegasus Knight, just like Fury, and so on. Averted with Patty, Nanna and Altenna. Interestingly, many of the sons take the class of the first generation male character that is "most likely" to be canon.
Meanwhile, in Fire Emblem Awakening, any children born to Nowi, Nah, or Tiki will always be female. All three being Manakete may have something to do with this, but the fact that male Manakete have been shown before in the franchise makes this unlikely. Though the reason for this is actually due to gameplay reasons. Nowi always gives birth to Nah, and all three can give birth to Morgan, but only female Morgan as she will always be male Avatar's child.
Averted in the same game by Panne, a Taguel (Rabbit Person). While she is the only one of her kind, her child is always a male. She has a male and a female if the Avatar is her husband.
In the series, the race of the child is determined almost entirely by the mother, with few of the father's racial traits making it through (with certain, often important exceptions). The Argonians are the only race not to share evolutionary origins with the others and are mutually infertile with everyone except each other, while Khajiit happen to be directly related to Wood Elves, with certain types of Khajit being virtually indistinguishable from them.
The ending of Grandia shows Justin and Feena several years later, married, with a bunch of little-Justins and little-Feenas running around.
The Gerudo from The Legend of Zelda: Ocarina of Time... maybe. The Gerudo are an all-female tribe of desert bandits that produces a male every one hundred years. In order to procreate, they visit Castle Town to meet Hylian "boyfriends". It's possible that the union of a Gerudo woman and a Hylian male produces either a female Gerudo or a male Hylian, but other than the above information there is no evidence of this in-game.
In Sa Ga Frontier 2, Cordelia (called Cody by Wil) is Wil's initial love interest and the mother of Wil's son, Rich. Depending on the player's choice, though, Cordelia can die, leaving Wil to marry Labelle instead. However, despite obviously not being Cordelia, Labelle still gives birth to the exact same son.
Averted in Solatorobo: Felineko and Caninu can interbreed, but the children are either Caninu or Felineko with no regard to gender.
Lampshaded in The Class Menagerie web-comic, where gender and species are explained as being based on that of the parents.
Averted in Kevin & Kell — while still managing to fail biology —, in which little Coney, daughter of a female wolf and a male rabbit, is an omnivorous bunny; she's mostly represented in the strip as being carnivorous, much to the surprise of a lot of her prey, but she can and does eat vegetables as well.
Jyrras and his sisters. Their dad is a kangaroo mouse while their mom is a kangaroo. Yes, he gets glomped a lot by his much bigger siblings, why do you ask?
Though when beings and creatures (demons, cubi etc.) interbreed their offspring look like their being parent with creature traits tacked on, regardless of gender. For example Lorenda is a half-demon cow, her mother is a demon mare and her father was a bull being. Likewise both Dan and Abel heavily resemble their being parent, and Dan's hypothetical daughter with Matilda, a taur Mythos, strongly resembles her mother.
Inverted in Precocious, Bud is a Scottish fold like his mother, while his older sister is a white American shorthair like their dad.
Somewhat justified with chakats and skunktaurs in the Chakona Space stories. They're both hermaphroditic species (though chakats are parallel and use more feminine terms, while skunktaurs are sequential and tend to be more masculine) and their genes are dominant to most dioecious species that they are compatible with. And when they interbreed their cubs are the same species as the mother, making it possible for a chakat to have a "brother" who is the same species as hir father, but a skunktaur's "sister" would be like hys father.
In general this is something that pops up frequently in the Furry Fandom when an artist/writer doesn't want to bother too much with genetics if two races can cross-breed at all.
Family Guy: Herbert's dream sequence parody of "Somewhere That's Green" from Little Shop of Horrors. In it, Herbert is dressed like Audrey and Chris is his Seymour. And the son and daughter look like Chris and Audrey!Herbert respectively. It's really weird compared to where the parody came from which shows that Seymour and Audrey's children look like miniature versions of their parents.
Goof Troop: Pete (a cat) and Peg (presumably a dog)'s children. P.J. looks just like Pete (with less of the ugly), and their daughter Pistol looks more like Peg. However, given that the majority of the characters in the show are Dog Faces and the concept of "breeds" does not seem to exist in the Goof Troop continuity, Pete may in fact be a dog in this series, making this an example of the supertrope Generation Xerox.
Played with in Rocko's Modern Life, where the children (born from an egg) of Filburt the turtle and his feline wife Dr. Hutchison follow this trope, except for one child being a steer who resembles Heffer who actually sat on the egg until it hatched (a Shout-Out to the Dr. Seuss book Horton Hatches an Egg).
Inverted in The Amazing World of Gumball: Gumball is the same species as his mom (a cat), his sister is the same species as his dad (a rabbit).
Hinted at in a painting that Painter Smurf had created of Papa Smurf and his prospective bride Flowerbell the woodnymph in The Smurfs episode "Papa's Wedding Day", with their offspring male Smurfs. The painting was done to dissuade Papa Smurf from marrying Flowerbell, as the other Smurfs knew the whole thing was a setup.
Averted in The Fairly OddParents television movie, Channel Chasers, where in an improved future shows a grown-up Timmy (who has married his Abhorrent Admirer Tooty), with two children; Timmy s' son looks like him, but wears a different hat, has black hair like Tootie, and a pointy nose. Timmy s' daughter looks like a female version of himself, with better teeth and tweezed eyebrows, and wears similar sunglasses and clothes to Tootie, and has a hairstyle similar to Timmy's childhood crush Trixie (as Timmy's eventual marriage was meant to be a secret at this point)
Regular Show: Margaret is a red robin like her mother (and the rest of her extended family, save John) while her father is a human.
Hobart's puppies in Dogstar. The girl puppies look exactly like their mother Lady, while the boy puppy looks exactly like Hobart.
My Little Pony: Friendship Is Magic is surprisingly good with this. Nine out of ten ponies do not directly resemble their parents. A few ponies (Rarity and Pumpkin Cake, who both look like their fathers) significantly resemble a parent, others share apparent physical traits (Sweetie Belle is white like her father, Rainbow Dash has her fathers hair and Pinkie Pie has her mother's eye color), and many more seem to instead resemble relatives (Applejack and Apple Bloom are shown to look like distant aunts).