just as the title, my question is can it possible for a creature that can reproduce with any/all creature despite it was different species/family? (not the alien xenomorph or parasite one/way but real interspecies reproduction activity) either as the one that do it or the one that giving birth/lay eggs.

the children can be mix of the parents gene, think like half-human, half-elf, half-dwarf, half-orc, etc. usually this is from human interacial/species (just an example) but the creature not necessary to be human or inteligent though.

what kind of genetic or reproduction organs to achieve it? (not restrict to only have single reproductive organ) outside of they are from the same universal anchestry/genetic handwave.

and will the half breed gonna be infertile or fertile? what kind of side effect to their genes?

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    $\begingroup$ Give a look at this. $\endgroup$ – Victor Stafusa Oct 13 '19 at 12:13
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    $\begingroup$ You appear to have specifically excluded all the possible options (gene stealing (aka the xenomorph trope) & parasitic or symbiotic (essentially same thing, only real difference is is it mutually beneficial or not) to achieve anything that might approach the desired result? $\endgroup$ – Pelinore Oct 13 '19 at 15:17
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    $\begingroup$ You have to limit which creatures it can breed with. There is no way for a thing to breed both with bees and with elephants using same reproduction organs. $\endgroup$ – Alice Oct 13 '19 at 22:04
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    $\begingroup$ Then you can't do it, sorry. $\endgroup$ – Alice Oct 13 '19 at 22:15
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    $\begingroup$ @Pelinore has a crusade now to demostrate that what OP wants is imposible. If someone change his mind, I would send a bounty. $\endgroup$ – Malkev Oct 14 '19 at 9:39

Based on our current understanding of reproductive biology it is not possible.

Each parent, in sexual reproduction, supplies half of the entire genetic set, which is then paired and used to build up a new organism.

To have two matching halves it is necessary that both parents have the same number of chromosomes: just look at what happens when, in humans, one gamete supplies an additional copy of chromosome 21. Incidentally, other trisomies can happen, too, but they are less likely to not heavily interfere with the fetus development.

Even assuming that there were the same number of chromosome, you would then need compatible biomolecular mechanisms to allow egg fecundation and fetus growth. Again, molecular keys are very selective for the very purpose of protecting a cell from outside environment.

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    $\begingroup$ The question states that the universal creature could be the one giving birth/eggs: so this creature could have internally a collection of all the chromosome configurations of the planet, and when reproducing it would only halves and updates its human DNA or its rabbit DNA or horse DNA (etc.), leaving the rest intact for the child. $\endgroup$ – Cœur Oct 13 '19 at 13:39
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    $\begingroup$ Apparently, Mew has the DNA of all other Pokémons. $\endgroup$ – Cœur Oct 13 '19 at 14:17
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    $\begingroup$ @Cœur : "The question states that the universal creature could be the one giving birth/eggs" : It also excludes the gene stealing trope as an option which it seems to me precludes any mechanisms for that in a science based answer. $\endgroup$ – Pelinore Oct 13 '19 at 14:44
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    $\begingroup$ This is not true, some bacteria, and algae use horizontal gene transfer as means to reproduce or "evolve". When using horizontal gene transfer anything is up the table again. $\endgroup$ – paul23 Oct 13 '19 at 23:02
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    $\begingroup$ @paul23 : horizontal transfer can only really be considered as part & parcel of the whole xenomorph gene stealing schtick, the mechanism by which it's achieved, as such the OP has specifically precluded it as an option to achieve what he wants. $\endgroup$ – Pelinore Oct 13 '19 at 23:44

Yes but.

You have to abandon the literality of this requirement:

The children can be mix of the parents gene

because there is no way of doing that, unless the creature has a complete genetic reengineering laboratory onboard. Just think that some creatures have a given number of chromosomes and genes, and other have different numbers. What would, or could, our xeno genes' be coding for? (As @Pelinore points out, this is what Orson Scott Card's Wyrms do - they reengineer a new copy of DNA holding both the host's and the guest's code entire, then use the host's, or a rearrangement thereof, to build the body).

Also, to be able to breed with other creatures you need the equipment. Pigs have corkscrews [thanks @Separatrix for the correction], ducks have worse, other creatures have (detachable) hectocotyla, sperm packets, fixed-shape and variable-shape phalluses, and so on. Then there's the matter of size. And then there are egg-layers. There is no way a single being can be physically compatible with more than relatively few other different species.

So we find an alternative. Turns out there already is one.

When you say "the children's genes" you're thinking of a child organism. But the child organism is a complex structure, and by rights its whole genetic code does not come all from the parents. By mass, perhaps four fifths do. But the rest is made of commensal organisms such as gut bacteria or tiny skin parasites/symbiotes.

Also, while 50+50% of the core DNA comes from the parents, the mother also contributes mitochondria. These are "sister" organisms with different DNA that penetrated our cells many million years ago, and instead of being digested, struck an "agreement" - they would supply a more efficient way of producing energy, and in exchange they would be able to dwell inside our very cells and take what they needed. Food and lodging, in other words.

In a healthy organism, mitochondria outnumber human cells by more than one thousand to one.

We are now already a hybrid of "human" (48 human DNA chromosomes) and "mitochondrion". Only we've grown so dependent on our guests that there can't exist a mitochondria-less human - they would die in very short order (cyanide poisoning does this).

So, what has happened once might happen again.

What our "creature" could do is infect another creature's cells and either replace their mitochondria or live together with them. The creature would also live in the host's neurons, as they are cells like any others, which means that the result could be as much "creature" as "host" - their joined mind would co-evolve if infection took place upon conceiving.

Intra- and inter-cellular communication would allow the xeno organism to be a single organism instead of a collection of disjointed cells.

The hybrid would breed true - a twist could be that the creature could trigger parthenogenetic pregnancy, meaning that a female could have sex with another female and get her pregnant, "half" the baby's inheritance coming from the human mother which would give birth, and the rest from the alien.... "mather"?'s xenochondria.

The difference shown by a hybrid might be none to all of the following:

  • different physical strength and intelligence (both more and less could be justified).
  • different tolerance to poisons and toxins (ditto, but very probably in the same direction as above - i.e., either stronger and more resistant, or weaker and less resistant)
  • different tolerance to heat, cold, fatigue, hunger and dehydration
  • different pregnancy duration
  • phenotypical changes, such as skin color and texture or body fat and proportions
  • sensorial changes (e.g. better/worse tactile sense)

Infection of an adult would probably only entail the first three set of changes, and possibly behavioral changes, even radical ones up to and including shuffling around murmuring "braaaiinnnnss....", when the infection reaches the frontal lobes. Or it could also of course mean death.

Some stories relating to this are Brin and Benford's Heart of the Comet (1986) with Saul's cyanutes, and especially Walter M. Miller Jr's Dark Benediction (1951); both describe this kind of endosymbiosis. A more parasitical kind, ending with the host's demise, is described in Greg Bear's Blood Music (the short story).

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    $\begingroup$ Seems very much like the parasite option excluded by the question? $\endgroup$ – Pelinore Oct 13 '19 at 15:08
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    $\begingroup$ @Pelinore I had interpreted "parasite" as in Orson Scott Card's "Wyrm". This could be more a symbiote. Actually it could never be a pure parasite, unless it could survive without a host (sort of Damon Knight's "four in one" maybe?) $\endgroup$ – LSerni Oct 13 '19 at 16:38
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    $\begingroup$ What The Wyrms are doing is preserving their own 'DNA' entire & camouflaging it inside a body built by following the DNA instructions of another, that's a gene stealer trope if I ever saw one :) 3/3 $\endgroup$ – Pelinore Oct 13 '19 at 17:22
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    $\begingroup$ @Pelinore weeelll... actually, Card's "explanation" of Imakulata genetic setup does not really make sense (at the beginning, in Prince Whatshisname speech to the princess, the one where Patience cuts her own neck, it is even said that the DNA "responds to men's will"). But yes, on second thought, the Wyrms do gene-stealing, which is what I answered not being really possible. $\endgroup$ – LSerni Oct 13 '19 at 18:11
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    $\begingroup$ An in book characters knowledge doesn't have to be accurate & it's often better (for the story) if it's not so we can't rely entirely on what any of his characters say in the book, that aside, iirc he was referring to selective breeding & saying it worked much faster than records suggested it used to back on Earth ... 1/2 $\endgroup$ – Pelinore Oct 13 '19 at 18:29

Some viruses get close to that.

According to a study, about 145 genes in the human genome have been received from other species through a process called horizontal gene transfer.

Retroviruses are a kind of virus that reproduces by splicing their genes into the host's chromosomes. Some well known viruses of this kind are HIV, FIV and FELV.

Retroviruses insert their genes in random locations of the host's chromosomes, and sometimes a mutation happens during the splicing which causes the new viruses generated by the host cell to come up with an extra gene it got from is host. If the virus happens to infect living beings of multiple species, this mechanism may cause some host to receive genes from a previous host of a different species. All that is required for this to happen is:

  • Proper contact of the kind the virus needs, between individuals of different species;
  • The two species having the same kind of cell receptor that allows the virus in;
  • The recipient species must also be infected in cells involved with reproduction.

This happens rarely in the most complex beings, and according to the study I mentioned it happens extremely rarely in humans. But it did happen in the past, and it seems like we got gene transfers in this fashion from fungi, bacteria and other animals this way!

In other words, some viruses reproduced within different beings of different kingdoms, taking some genes from their hosts and leaving some of their own in the process. This is rare, and usually any given virus will only affect a small set of species. But there is always the possibility that some retrovirus acquires the same promiscuity as Influenza A, which can probably infect all birds and mammals (it has been found in whales, seals, horses, pigs, chicken and seagulls). It could cause some interesting changes in any given ecosystem (not as spectacular as you are probably thinking but still...).

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    $\begingroup$ Interesting & mostly accurate (to the best of my understanding) but doesn't really approach an answer to the OP's question? $\endgroup$ – Pelinore Oct 13 '19 at 18:03
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    $\begingroup$ Not just viruses. Some bacteria can swap genes with other bacteria - even from a different species. This works a bit like mutation but instead of a random change/damage the process involves random splicing making it far more likely than mutation to transfer features/abilities such as antibiotic resistance $\endgroup$ – slebetman Oct 14 '19 at 1:21

maybe an organism that works as a sort of cloning device. it would somehow replicate the genetic material, and then cause a fetus to be born. it would create clones of the thing that copulated with it, not an inter-species clone.

  • $\begingroup$ thats what i think at first base of ditto from pokemon, but i assume it wont generate half breed right? $\endgroup$ – Li Jun Oct 13 '19 at 9:12
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    $\begingroup$ Unless it does some gene editing to insert DNA for its own reproductive system it's going to go extinct in short order, or rather the ability to breed with anything is. $\endgroup$ – Pelinore Oct 13 '19 at 14:47
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    $\begingroup$ Also, copulation isn't going to get it the material it needs to clone it's 'partner' from, it's going to need to do some impressive gene editing to splice the DNA from two sperm together to get one set of working DNA, which may cause problems, a lot of genetic diseases are the result of two copies of this or that. $\endgroup$ – Pelinore Oct 13 '19 at 14:51
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    $\begingroup$ Also sounds bit close to the bone to the genestealer trope excluded by the question? $\endgroup$ – Pelinore Oct 13 '19 at 14:54

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