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Imagine a child of mixed race, one parent is human and one is an alien who has some ability humans do not have, for the sake of argument telepathy. I'm assuming there is some advanced medical assistance to allow the mother to conceive at all.

I'm interested in what would happen to the ability only one parent has. The closest earth example I can think of is a quagga (half zebra and half horse). In this case the stripes do not cover the entire body of the offspring. This indicates to me that the genetic trait would only be partially passed on.

Which of the four options are most likely (or have I missed one?)

  • The child would not inherit the parent's ability
  • The child would inherit the parent's ability
  • The child would partially inherit the trait resulting in a scaled down version (empathy instead of telepathy)
  • The doctor who aided the parents conceive would decide which traits would be passed on and which wouldn't.
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    $\begingroup$ Quaggas aren't half zebra half horse, they're a distinct species. Zebra/equine hybrids are referred to as zebroids: en.wikipedia.org/wiki/Zebroid $\endgroup$ – ckersch Feb 5 '15 at 15:26
  • $\begingroup$ @ckersch you're right - I was thinking of a programme I watched where they were attempting to re-bread quaggas $\endgroup$ – Liath Feb 5 '15 at 15:27
  • $\begingroup$ I'd think the most likely option would be like with the Asari, and the kid just gets all of the genes from the mother, spruced up in some way or another by the non-Asari. $\endgroup$ – DaaaahWhoosh Feb 5 '15 at 15:58
  • $\begingroup$ Related: Would co-orbital planets with very similar convergent evolutionary paths be possible? $\endgroup$ – a CVn Feb 5 '15 at 19:06
  • $\begingroup$ Heh. Were fried quagga a delicacy? The answer to your question lies in this: "How is the trait of interest stored?" If it's an organ, than out will require an entire series of gene to enable it. Unless the other parent happens to carry the requisite structures to support it even if not present in the race, the trait might even be expressed but useless. (Or out might not even be expressed.) There is no science-based answer, really, but the best is that either the same magical force that permits fertility also makes the traits work, or the differences are so dramatic nothing happens. $\endgroup$ – The Nate Feb 26 '16 at 10:29

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If the alien is truly alien, not some variant human in space, it is highly unlikely to be able to have children with humans. It would not be like horse and zebra, it would be closer to a horse trying to breed with a tree or a fungus. As such the offspring would basically be a genetically engineered artificial lifeform based on the traits of the parents. Thus it would be up to whoever did the design to decide what traits and systems to take from each parent. In practical terms that would be you.

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    $\begingroup$ I disagree that it would be like a horse trying to breed with a fungus. It would be more like a horse trying to breed with a river or a computer program. $\endgroup$ – Mark Feb 5 '15 at 23:40
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    $\begingroup$ No amount of genetic engineering can overcome situation if both organisms do not use same genetic coding. $\endgroup$ – Peter M. Feb 6 '15 at 1:06
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    $\begingroup$ What about some kind of fusion? $\endgroup$ – user2547 Feb 6 '15 at 3:18
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    $\begingroup$ @Mark - both horse and fungus are practically the same: both are eucaryotes. Even Bacteria and Archea are more different from each other than horse is from fungus. Just check the link. It will be more like breeding the horse with digital clock or tuna sandwich. :-) $\endgroup$ – Peter M. Nov 17 '15 at 19:32
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    $\begingroup$ @Aron That the crossbreeding happened is the premise of the question. My point was that since it would be an extremely difficult feat by definition, manipulating the "inheritance" to your preferences would be trivial in comparison. Not sure why I get so many comments pointing out that this crossbreeding would be extremely unlikely to be possible, tbh. A premise is a premise, we simple have to assume it is possible and adjust our other assumptions to match. $\endgroup$ – Ville Niemi Aug 24 '16 at 6:29
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You assume that alien's inheritance is guided also by DNA. It is very unlikely that on another planet, under very different conditions, life would evolve to use the same rather complicated mechanisms for inheritance: ATCG for DNA, proteins to guide transcription, etc. They are all complicated and co-evolved to work together. It is like a very complicated dance, with chemical signals passing back and forth.

From the point of biology, humans, animals, plants, and fungi are very similar - all are eukaryotes - even on Earth are many organisms (prokaryotes and archea) which are radically different from eukaryotes, (IOW more different than the difference between an animal and a plant) even if they use the same DNA mechanism for inheritance. For instance, many bacteria do not have sex, but are able to exchange plasmids (which contain some DNA info, but not as string like chromosomes of eukaryots, but as rings), directly. Alien world indeed. Interbreeding a plant and animal would be substantially easier than interbreeding with alien non-DNA life-form.

Even in humans, sometimes proteins misfold and cannot function. Or function, but wrong way. Tha's why we have so many genetic diseases. And miscarriages, when embryo is not viable (chemistry is broken in a subtle way). When cell is dividing, different biochemical signals sent to neighboring cells guide development of different organs. Wrong signal will cause errors on development of organs, and embryo could die or misform.

The only way would be if life on both planets was seeded by some elder race to use same genetic mechanism. Even then, after few millions of years of separated evolution, species would not be able to cross-breed naturally. This happens even on Earth. If both species use exactly same biochemistry for genetics, you might be able to artificially inject genes from one species to another. It is a crap shot, and in most cases this infusion will destroy some biochemical signals or another. Gene expression is very delicate process and there is lot what can go wrong and cell is doomed.

So it is your world, and you can postulate that it is so, but such situation would not evolve naturally - only in a Hollywood script.

Also, some viruses - retroviruses - spread by adding they own RNA to cell's. And cells have all kinds of mechanisms to prevent that. So when someone would want to add alien DNA to the cell, cell would fight back - and has millenia of success to count on. Big chunks of human DNA is suspected to be retrovirus genes injected, but disabled, during evolution. It is much more complicated than you imagine.

(I guess my answer not accepted, too much technical details about the real complexity of the problem :-)

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All of the above are possible, and in fact plausible.

The most likely answer is actually your final one, in that the doctors designing the new life-form (because that is essentially what they are doing) would choose which traits were important from each parent. There may be compatibility restrictions though that mean they they are forced into choosing one in particular of the first three instances. As the person designing the universe you could choose those constraints, so if you want a certain option but don't know why they would choose it then they could be forced to make that choice for biological compatibility.

Note that alien->human telepathy is highly unlikely from a reality-check perspective unless the human has some augmentations (for example implants) to support it.

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The child has a 100% chance of having no abilities except nonexistence... unless the alien parent is really nearly human genetically... or unless the child isn't a child the way Earth creatures reproduce, but is the product of some other alien process.

Zebras and horses can breed because they are almost the same animal. Humans can't breed with practically any other Earth species - maybe with chimpanzees. That's because we are related to them. We wouldn't be related to aliens who evolved on some other planet, unless we are (because humans or primates were dropped here by space aliens long long ago), but even so, the chance of our DNA being similar enough to produce viable children is low. But if somehow our DNA is similar, then see genetics-based answers, except it would depend on the trait you are interested in, and how many genes are involved, etc.

Another possibility is that non-human aliens, since they probably wouldn't reproduce like humans at all, might have some other reproduction abilities that would make a "child" possible, but it might really be a human clone, human clone with mutations, or something else very bizarre, such as the xenomorph in The Thing, or as in Alien, or something else quite, quite alien.

Also, as others have pointed out, genetic engineering might be necessary and could stack the deck, but then you are talking about technological abilities by design, and since those technologies don't exist, we can't know the chances of outcomes (and so as authors we can make them up without fear of breaking anyone's disbelief except that the technology would ever exist or be used).

Finally, in the case of telepathy, it's pretty clear humans and most/all other Earth species already have telepathy. Most of us just don't use it, aren't aware of it, or actively aggressively ridicule/disbelieve it.

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Based on Mendelian genetic system, the genome should be in pair.

For example if ability to telepathy is a dominant trait:

TT -> able to do telepathy

tt -> unable to do telepathy

Human (tt) X Alien (TT)

The result: Tt, Tt, Tt, Tt -> 100% Tt

It could mean that they would still have the ability. But in some case intermediate trait occurs. Intermediate trait means that the trait is mixed. So it could be decreased ability (such as unable to do telepathy with anything over 50 meter or anything like that).

Another thing to consider is that in the example above I assume that the ability is a dominant trait. What if it's a passive trait? If it is, then the breed wouldn't be able to do telepathy at all.


Summary:

  1. If the ability is a dominant trait, then the breed would be have the ability

  2. If it's an intermediate-compatible trait, then the breed would have the ability, but with decreased effect

  3. If the ability is a passive trait, then the breed wouldn't be able to have the ability.

Remember: Positive trait is usually the dominant one.

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    $\begingroup$ I thought about this approach, however I assumed that telepathy/the ability to change colour/mind control or whatever was likely to be a combinations of lots and lots of pairs rather than just a single one. It's not like our DNA has switches which say "yes to make this person blue" or "deactivate unlimited healing" $\endgroup$ – Liath Feb 5 '15 at 11:53
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    $\begingroup$ It might not be this simple, but remember that the intermediate trait exist as the implication. $\endgroup$ – Kristian Feb 5 '15 at 12:09
  • $\begingroup$ What if the alien is not diploid at all? $\endgroup$ – JDługosz Nov 17 '15 at 1:18
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I would say the most likely is #4, because you already need the doctor to even make it possible and to ensure you don't get some twisted little monster. So while doing all of that, they might as well take the time to pick and choose the other traits that will be showing up as well.

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While it'd be impossible for alien DNA (if they have DNA) and human DNA to mix, you can do it in different ways in your story:

  • Half-half: So, if an alien is a telepath level 10 (let's say) the human-alien child would be a telepath (level 5). If the alien race lacks some human trait, the hybrids might inherit it. Look at Spock: he's got the Vulcan mind meld and the human capability to feel emotions.
  • Random degrees: Maybe one child is a strong telepath, other is just a weak telepath but has astral projection powers. Maybe some of the hybrids are super-strong while others are weakened by their inheritance.
  • If your alien race has many super-human attributes, some children might inherit just one trait (super-strength), while other hybrids inherit another one (telepathy), while other are just a bit stronger and a bit telepathic.

While human-alien DNA mix might not be scientifically feasible, most readers will give you suspension-of-disbelief as long as you are internally consistent.

I just thought of something else: you can establish that not all hybrid offspring is viable.

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Assuming that alien-human breeding is like human-human breeding in your world...

If having powers is a recessive gene and not having powers is a dominant gene, the child has a 100% chance of being a carrier for powers but not expressing them (Nn).

If having powers is a dominant gene and not having powers is a recessive gene:

If the alien has Pp as his genotype, the kid will have a 50% chance of Pp and a 50% chance of pp - a 50% chance of having powers and a 50% chance of not having powers.

If the alien has PP as his genotype, then the kid will have a 100% chance of Pp and will have powers but will be a carrier for not having powers.

If alien-human breeding isn't like human-human breeding, it's really up to you how it works, and, by extension, what the outcome is for the powers.

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Number 4. You underestimate the difficulties involved in cross-species conception. Everyone does, because half-alien kids make for very interesting storylines, but now you're asking to bring real science to the party. And the real science is not kind to hybrids. Organogenesis and the general development of the embryo is so fantastically complicated that a hybrid is essentially non-viable.

The only way to do this is to presuppose the existence of medical technology far beyond ours, capable of designing a hybrid organism and essentially coding the directions for "how to build this creature from an embryo" from scratch. Such technology implies a genetic engineering capability equal to or beyond that what you would need to say "Here is a blueprint of exactly what I want this child to look like, go figure out how to build it."

Also, this technology will need to work well enough to be successful on - perhaps not the first attempt, but certainly before the hundredth. That means that even though such a thing might have never been done with an alien before, the doctors certainly will have to have extensive practice with the general techniques. Either that, or the origin story of this child will involve a hundred failed attempts.

Anyway, the long and short is, the technology to do this at all requires as a prerequisite the technology to bring about option four.

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  • $\begingroup$ While this is true, it doesn't seem to add much to what this answer or the accepted answer already say. Yes, there are a lot of similar answers, but most of those were posted around the same time. You may find it more effective to look for newer questions to answer with similar insight. Oh, and welcome to Worldbuilding. $\endgroup$ – Brythan Aug 24 '16 at 1:35
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5th Possibility

Both the alien race and the human race are inhabited by the same life-driving force (the one that tells the reproductive codes what to do, whichever kind they are).

In this way, the alien material organism is gathered together by a self-aware form of the life force, and the human material organism is built by either a non-self aware or self-aware form of the life force.

The alien form that is definitely self aware finds a way to meld with a human form and then proceeds to direct the human reproduction using the human dna coding system. Since it is fully self-aware it will be able to select which traits to pass along to its offspring, including the coding needed for the desired ability to be expressed at whatever level it chooses. It is similar to option 4, except it is the alien life force directing it's own effects, not a doctor.

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I'm assuming, based on the goldilocks theory, I would say any extra solar life forms would be humanoid, thereby a high likelihood of being compatible. Telepathy is considered a higher brain function, we already know we have the ability to emit signals from our brain. Any being with the other half of that ability that allows them to receive the signals and interpret would be more highly evolved thus their genetic contribution would be more dominant, for that reason I would say the ability would not be diluted but more the offspring will either be born with the ability or they will not.

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    $\begingroup$ I don't follow the logic here. The "Goldilocks zone" says nothing about what type of life would develop. Telepathy is also not necessarily a higher brain function; any creature could evolve to have it. $\endgroup$ – HDE 226868 Nov 17 '15 at 0:53
  • $\begingroup$ The Goldilocks zone theory is based on the optimal composition that is required for humans to exist on a planet other than Earth. How is that difficult to follow? $\endgroup$ – Foyz Aug 15 '18 at 12:15

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