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It’s the age of genetic engineering, and Scientists, in league with shady corporations, have created a group of human-animal hybrids, hereafter referred to as Metamorphs.

Metamorphs are designed as slave labour; since they are nonhuman, human rights don’t apply to them. However, some buyers may wish to use their Metamorphs for breeding purposes, which leads to the risk of human-Metamorph hybrid children that could present serious legal backlash. For plot-related reasons, I don’t want the Metamorphs to be made infertile with humans, so I have devised a solution that means that Metamorphs produce only human children when paired with humans:

As any geneticist will tell you, there are dominant genes and recessive genes. The animal half of the metamorph genome has been made “hyper-recessive”, so that when paired with a human partner, the animal traits are not expressed in the offspring. The animal genes only express themselves when paired with another metamorph.

Is this a plausible solution from a scientific point of view, or no?

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  • $\begingroup$ This is a good way to ask Worldbuilding questions. Explain the rule of your world and ask for help rationalizing it. That's our sweet spot. $\endgroup$
    – JBH
    Feb 18, 2023 at 16:10

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No. Also, you have a contradiction in your metamorphs

You said that Metamorphs don't have human rights because they don't count as human. But here lies a problem: by definition they ARE human if they can produce viable offsprings with them. From wiki:

A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction.

You have to understand that introducing serious changes would quickly result in non-viability of children when pairing with baseline humans. More or less ANY chromosomal changes would lead to infertility (in metamorphs-human pairs, metamorphs-metamorphs pairs could still be made fertile). And even if you keep the number, size and genetic makeup of chromosomes more or less the same, introducing too many changes to the genetic structure would lead to same issue. So your problem is that if the change is small enough for them to have viable offsprings with basaeline humans they would still count as humans, but if the changes are larger, they wouldn't be able to be bred with humans.

And even if relatively small changes (where you could have an issue telling metamorphs apart from humans) can introduce issues, so them having the ability to mate with humans would have to be made on purpose (and not easily). Which goes against your motion that those offsprings would face legal backlash. And required level of genetical modification for such a thing would be high enough that such society could create servant race without human parts (well, they could look human on the outside). Which would be far easier to sell to the population and lawmakers - but sadly, no viable metamorphs-human hybrids in that case. Not that that would stop certain people from engaging in sexual activities with metamorphs, social taboo or not, it just wouldn't produce offsprings.

Also, you have some misunderstanding of recesive/dominant genes. You have 2 (or multiple) copies of the SAME gene. And that same gene can have multiple variations, some of which can be called recesive and some dominant. But it is still the same gene, it encodes practically same protein with practically same function. So you generally can't have different functionality on your recesive genes (there are exceptions, as always in biology, but they are rather rare). Not to mention, most atributes are determined by quite a lot of genes that interact with each other, so that clear recesive/dominant divide is not all that common (Mendel was extremely lucky with his choice of atributes).

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  • $\begingroup$ >You said that Metamorphs don't have human rights because they don't count as human. But here lies a problem: by definition they ARE human if they can produce viable offsprings with them ---quote end--- I think they meant legal definition of human rather than scientific definition of human when designating human rights. $\endgroup$
    – Harry Mu
    Feb 18, 2023 at 23:43
  • $\begingroup$ @HarryMu You are under asumption that there is no connection between scientific and legal definitions. Because they are. And this is not a definition that is obscure, it is something children in elementary school learn, which mean ignoring it is harder. $\endgroup$
    – Negdo
    Feb 20, 2023 at 7:50
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    $\begingroup$ I mean historically, scientific and legal definitions were pretty much random. Like the 3/5ths thing in the US constitution. There is no reason for a government to honor a precise scientific definition if it is not useful or otherwise beneficial. $\endgroup$
    – Harry Mu
    Feb 20, 2023 at 15:29
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Simple Answer: No

There is no such thing as "hyper-recessive" genes. The nature of earth-based genetics are that there are two of each gene, one from each parent. If all "metamorph" versions of a given gene are recessive, then the offspring of a human and a metamorph will be a human, but their offspring will show metamorph traits if they mate with another human/metamorph offspring or a metamorph.

Put simply, math says that your plan doesn't work. If the genes are recessive ("hyper" or otherwise), then any Metamorph must be homozygous for every gene, and must pass those genes on to their offspring, setting the genes up for expression in the next generation.

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    $\begingroup$ Ehhh sorry disclaimer: this is recall from an AP bio class years ago so this is more than fuzzy, But IIRC some genes are unexpressed because the body did not need to use it for a long time or that the genes were bound too tightly for transcription proteins to access. Its possible to cause even dominant genes to go by those mechanisms. as for relevance to the topic at hand, I'd still agree with you but there are technically different types and varying degrees of recessiveness, depending on how you cut the cake. $\endgroup$
    – Harry Mu
    Feb 17, 2023 at 4:07
  • $\begingroup$ Not all genes have strict dominant/recessive pairings: en.wikipedia.org/wiki/Dominance_(genetics)#Incomplete_dominance $\endgroup$ Feb 17, 2023 at 14:45
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    $\begingroup$ @Harry Mu - this is true, but also even less what the OP wants. Genes that are unexpressed because of antiquity are not available when the right circumstances (ie. a metamorph-metamorph pairing) arise, they're halfway to being junk DNA. They definitely will not behave in the fashion desired (that is, akin to a recessive gene.) $\endgroup$
    – jdunlop
    Feb 17, 2023 at 18:14
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    $\begingroup$ @SarahMesser - this is also true, but co-dominance or incomplete dominance are also not what the OP ordered. They want the gene not just to be recessive but effectively guaranteed not to be in the meiosis of a germ cell if paired with a human. $\endgroup$
    – jdunlop
    Feb 17, 2023 at 18:15
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Handwavy Answer : Yes

The Metamorph sex cells (MX=egg and MY=sperm) are a complete copy of DNA instead of only a single strand. Attached to this cell is a nanobot controller whose purpose is to maintain the 50/50 human-animal combination that has been found to be required for viable offspring.

When a MX combines with a MY, the accompanying nanobots link and begin the splitting and combination of the two cells to build the zygotes [1].

When a MX or MY combine with a human sex cell (Y or X, respectively), the nanobot has another function. When the human sex cell combines with the Metamorph cell, the lone nanobot still goes through the process of dividing the Metamorph cell, but it also filters the genes so that only a single strand of DNA remains, and that strand is made up of only 100% human DNA. The nanobot then expels itself and the excess junk DNA from the zygote, where normal bodily processes can dispose of them.

1: A side effect of this process is that two zygotes are produced (non-identical twin births being the rule for Metamorphs). If there are different types of Metamorphs (ie cat-people and dog-people) and two different types produce offspring together, then one of the children will be of one type and the other will be the other.

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Very handwavy but yea sure, just have two coexisting genomes with some caveats (caveats listed in text)

This is stretching the boundaries or biology in reality But if there were, say, two sets of genomes (human, morph) in each metamorph's cells it might... be possible?

Think of it like this. Its not genes that directly determines what we are, its how those genes are expressed. if a beaver were to have human genes in every cell but no relevant proteins to express that, the beaver is still a beaver, maybe with some extra cellular detritus.

So if a metamorph's specialized double duty egg or sperm hits the egg or sperm of a human, the human genes match up and create a baby and the morph genes get disregarded and flushed out in the process. But if morph-morph action happens, both genomes are completed and expressed accordingly.

So the metamorph DNA kinda acts like custom game mod or API that redirects proteins to express the intended metamorph state.

A technicality is that the metamorph exclusive genes need to be more like a DLC to the human genes and takes priority i.e. overriding human traits that would normally be expressed with human only genes. in that way if only morph genes are paired, the resulting baby is a miscarriage and animals won't be born.

This is very shaky and handwavy but imo it could work. The reason why it uses human genes but acts like a dlc can also be explained by its background from shady corpos in that some scientists had created a viable metamorph "DNA DLC" but wanted to manufacture a lot of those metamorphs so they made it so that the DNA DLC would be passed on from metamorph to metamorph but not to humans as to "keep the genes clean" or prevent "normal" human populations from declining due to the inevitable flings.

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As jdunlop has already explained in his answer, for a true Hybrid no, simply not how genetics work.

Howsoever.

If you drop the hybrid and go with some form of lab grown Chimaera instead then the answer could be a qualified yes.

As the cells making up the pertinent portion of the gonads or ovaries that produce sperm and eggs will be then either entirely human or entirely something else .. so your chimera will be able to mate successfully with the species corresponding to the genes of those cells and the offspring is going to be entirely of that one species.

Your chimera will be able to mate successfully with the species corresponding to those genes.

Well, at least with respect to sperm penetration of the egg cell and the beginning of cell division.

Physical ability to do so is another matter, depending on species one might be too large or small for the other to actively couple with it, and the 'equipment' might not be of compatible types of course.

Whether it feels any inclination to do so is of course yet another matter.

And womb environment can also be an issue when it comes to a developing embryo actually reaching term as the wrong species womb for the developing embryo may not (depending on species) provide a 'welcoming' environment for the developing embryo which will then die.

Things like body temperature and acidity of womb environment matter quite a lot and can vary considerably species to species.

But those are all issues that with careful choice of species used can be managed or avoided.

..

An alternative option is to surgically remove the gonads and ovaries of all your hybrids before sale and replace those parts with lab grown human ones of the buyers choice .. thus making them into chimera as well as hybrids of course.

Tissue rejection of the new gonads or ovaries can be avoided by 'inoculating' the hybrid against rejecting the chosen cell line for its new gonads or ovaries by simply injecting a small amount of cells from that cell line into it while in the womb before it's immune system 'calibrates' itself.

You'll find some link resources to help explain that 'inoculation' here.

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    $\begingroup$ This is true, but doesn't allow what the OP asks for - namely, that metamorphs be interfertile. The desired outcome is metamorph x metamorph = metamorph, metamorph x human = human. A chimera with gonads of one species or the other cannot produce viable chimera offspring. $\endgroup$
    – jdunlop
    Feb 17, 2023 at 1:00
  • $\begingroup$ @jdunlop no that's not what the OP asks for, the OP asks "that when paired with a human partner, the animal traits are not expressed" and that "the animal genes only express themselves when paired with another" of his 'hybrids' and this does that exactly .. especially if you give them one gonad or ovary of each type 🤗 $\endgroup$
    – Pelinore
    Feb 17, 2023 at 1:03
  • $\begingroup$ I think the spirit here is clear; they want another metamorph, not an animal. But if you insist on following the letter and not the spirit, fill your boots. $\endgroup$
    – jdunlop
    Feb 17, 2023 at 1:05
  • $\begingroup$ @jdunlop 😁👍 .. "they want another metamorph" which is exactly what they will get .. one 'metamorph' gonad (or ovary) and one human gonad (or ovary) in each will produce exactly that result .. presuming they are designed to be reproductively incompatible with humans on a genetic or sperm penetration of the egg level then they produce two types of sperm and only one type will work for each species of partner 🤗 can result in a pair of them producing a human offspring (roughly a 25% chance all else being equal) but you can avoid that by not performing the operation on any not sold for that. $\endgroup$
    – Pelinore
    Feb 17, 2023 at 1:11
  • $\begingroup$ @jdunlop 🙄 Oops, missed a bit out .. "which is exactly what they will get" with my alternative option. $\endgroup$
    – Pelinore
    Feb 17, 2023 at 1:19

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