Worldbuilding: Project Tatterdemalion and bio details

This is a reply to Lindenare’s and Beth’s posts a few days back. You guys are awesome. SF bio, hee….

WARNING: In-depth discussion of biological fertility here. Should be PG-13 at most, but there will be technical language. A glossary will be provided for the most esoteric terms, but I take no responsibility for any injuries incurred by frantically excavating your high school bio book out of storage. 😉

Glossary: Haploid: having 1 n set of chromosomes. Most higher organisms we’re familiar with are diploid, with a 2n set of chromosomes, and produce haploid gametes (sperm and eggs in most animals) to reproduce. Though technically salmonids (salmon, trout, others) are actually tetraploid, with one set of 2n chromosomes active in fresh water and another in salt (or wherever they spend growing up). And then there’s fungi and that can get really scary….

Macrocephalic: With a very large head. In this case, the “sperm” head.

Meiosis: Specialized cell division that, instead of producing 2 daughter cells that are 2n duplicates of the original cell, produces 4 haploid (1n) gametes. It often involves crossover, where chromosomes of each pair will literally twist around each other and trade pieces of DNA; anywhere from a tiny bit of a gene to most of a chromosome. This doesn’t always work correctly, and some gametes will end up with incomplete chromosomes or duplicate chromosomes. That… tends not to have good results. Really.

Methylation is the process of adding methyl groups to some areas of the DNA that serve to, among other things, either promote or block RNA transcription, thus affecting how the gene is expressed. (DNA transcribed to RNA translated to proteins is the common way to express a gene, though it can get much, much more complicated than that.)

Motile means “it can move”. It specifically refers to cells that can move, as opposed to larger organisms.

Polar bodies: Egg cells are formed by a specialized type of meiosis that boots out 3 sets of DNA while keeping almost all the cell organelles and energy in the remaining egg cell. Polar bodies are the 3 booted-out sets.

Tritiya gametes are haploid and motile. I think Beth has a great idea in amoeboid sperm, because, well, this dialogue comes to mind….

Isshin: “Wait, even those have tentacles?”

Yoruichi: “Pseudopodia.”

Isshin: “Tentacles. I’m calling it now.”

> Also, if fertilization can occur in tritiya + egg and tritiya + sperm combinations, why don’t tritiya + tritiya combinations work?

Wrong methylation on the parental chromosomes. Same reason you can’t currently make a viable zygote with two sperm cells or two eggs. Chromosomes get “marked” with what sex they’re from. Anything with two sets of tritiya chromosomes would get tossed as nonviable.

Also, it’s not a case of “can occur in this combo”, it’s a case of “has to have all of these combos to work”. Splicing in your DNA via a virus into existing chromosomes is not an exact science. There might be insertions that are viable enough in the somatic case (the infected person) but will fail utterly to generate a new organism from zygote on. It does take a lot of energy, but by using this method the Arrancar do 2 things: they guarantee low fertility (they want more spreading than natural offspring), but they also give resulting offspring the best chance by “weeding out” all the nonviable chromosomes.

No, I’m not sure exactly how the weeding out happens. It’s a combo of natural measures with the regular microtubules (protein structures that hook onto the chromosomes to move them), and “checking” the psychokinetic database Arrancar have set up for their new spawn. Complicated stuff like flash-step isn’t just instinct!

> For that matter, are the initial zygotes (diploid, 2n) motile at all,

They are motile. As for fusion – I suspect the sperm-egg 2n puts out the right signals for the other two to find it. Which means there are 6 copies of each chromosome in the superzygote, and they will pair up in three pairs, crossover indeed possible. Shinigami and youkai are three-sexed, but they are 2n chromosome count. From there, yes, splitting three ways; some of which hopefully would be viable.

>If we are assuming that the egg is still like a human egg and both the sperm and tritiya are small and sperm-like, then only the egg cell carries mitochondria.

That seems highly likely. After all, why mess with what works?

A tritiya cell might be carrying an X, Y, or W chromosome. It’s also likely carrying other necessities – not just other plasmid DNAs, but particular enzymes that say “right, not human, this is how splitting up the superzygote is going to work, people.”

>The entry of a sperm into an egg causes the membrane of the egg cell to change to exclude any additional sperm from entering. If this “new” membrane is what attracts the tritiya cell, then lack of sperm in the equation means that the triyata cell would be incapable of merging with the egg, again creating no offspring.

Ooo. That’s a good idea! At least for one of the combos to attract the other two. As for IVF tritiya-female offspring… I warn you the bunnies took a look at Soi Fon and Yoruichi and hid.

> If a single egg can create three viable fetuses in this AU than the two copies of maternal DNA are both needed.

*Nod* I’m actually thinking that this is a more a case of “tendency to fraternal twins” ramped Up to Eleven rather than saving one of the discarded polar bodies. As in, two eggs released. So there are actually 3 (1n+1n) combinations involved, that then fuse.

I do agree on the tritiya cell attracting sperm, although it’s likely to be a bit more… aggressive in actively finding it. Macrocephalic “sperm” definitely works.

>There will still be mistakes when packaging the DNA, and DNA imprinting will still come into play.

And how. Ouch. Once they realize fertility is possible, I suspect our geneticists will be wanted to check. Check everything.

> Both sides divide again, hopefully putting 3 DNA-sets in their own cell and leaving one empty ghost-cell. Any cells with more than 1 DNA set will not be viable. After this 4-cell division all 4 cells break apart via signalling from one of the tritiya cell plasmids and become up to three viable embryos.

Works. 🙂

>Now take a moment to stop and pity the poor mother who would have given birth to fraternal triplets if she had stayed fully human.

*G* Masaki had twins. I’m guessing twins could be relatively common.


30 thoughts on “Worldbuilding: Project Tatterdemalion and bio details

  1. Interesting . . . very interesting.

    One suspects that our mad scientists will be very busy trying untangle even the basics of this just to have an idea of how their reproduction works at all.

    Especially since part of how the Shinigami (and youkai) work might not be exactly how the Arracanar do simply because of the tinkering they did via the vaccine and whatever it is that Nii does and whatever it is that Sutra does (pro tip – pick Shinigami vaccine or the Sutra).

    Can’t blame the bunnies for wanting to hide from the idea of Yoruichi and Soifon . . . eeek.

    Not looking for spoilers but Orihime, Tatsuki, and Chad should be interesting in this setting. Not to mention Rukia and Renji.

    Liked by 1 person

  2. Ooff. Still, imagine what happens if you get a viable egg, and it splits? You have up to three fraternal offspring from the initial mating, but there is the possibility that the embryo splits, just like a regular human. It probably is a very minuscule chance, but there is at least one woman who had IVF and had both eggs take and split. When it comes to the human reproductive actions? We take stubborn in the womb and swap out extra womb time for more.

    Liked by 2 people

  3. I’ll admit about 80% of the genetics stuff went right over my head, but Yourichi and Soifon pregnant at the same time? Yeah. No. Even Urahara doesn’t deserve that! (Although the Arrancar might…)
    Not saying that female Tritiya shouldn’t be able to carry children, just saying that any triad having two members pregnant simultaneously sounds like a horrible idea (maybe they could take turns? Or if the female doesn’t want to/can’t carry children to term, the tritiya could be a surrogate?)

    Liked by 2 people

    1. I’m with ToxicSunrise. It’s been a while since I’ve paid much attention to to the mechanics of conception. I just recognize the terms from long ago Biology. One thing I do remember is that there is significant evidence that a mother’s body recognizes and disposes of non-viable fetuses quite ruthlessly. Miscarriages in early pregnancy are much more frequent than normally admitted. Most of the time, no one knows it has happened. The fertilized egg just fails to implant in the uterus wall.

      Liked by 2 people

      1. *nods*

        Because pregnancy is so resource heavy and risky (because the fetus / embyro ties itself directly into the mother’s bloodstream and thus can affect a variety of things including her blood pressure and it ups the risk of fatal bleeding – let’s just say that there are very good reasons that 1 in 4 women used to die in childbirth – and still do in certain parts of the world), the woman’s body does try to make it as difficult as possible for a fertilized egg to implant.

        And even when it does implant, making a new person is a complicated process and there are about a gazillion things that can go wrong. For example, at one point in fetal development, the heart is above where the bits that form head are and it doesn’t always slide down where it is supposed to be. Or it mistakes the umbrial cord as part of the intestines . . .

        Sometimes if you look at it closely, it seems amazing that we actually managed to get a world population of over 7 billion people.

        Liked by 1 person

  4. Huh… my brain has just taken a weird left turn…

    Since in this ‘verse we know that for Shinigami to reproduce you need three individuals, male, female, and tritiya, my mind instantly started asking ‘who’s the third parent of Ichigo and the twins?’ and then replied with Ryuuken as a willing donor of sorts to let Isshin and Masaki have kids – AND THEN decided that that would make Ishida and Ichigo twins, with Ishida given to Ryuuken to raise but for whatever reason Isshin and Masaki kept both Karin and Yuzu instead of one of them also going to Ryuuken. Maybe he decided he had his hands full with one kid?

    Liked by 2 people

    1. I like your logic, but we don’t need to follow cannon to the letter now, do we? Ex: perhaps the triad never splits? Or if we go the cannon route with Masaki’s death, the relationship between Isshin and Ryuuken could have collapsed upon her death, with Ishida following Ryuuken to complete his Quincy training while the more Shinigami-oriented children staying with their father? Or perhaps the split happened earlier in the timeline, when Masaki was pregnant with the girls? Lots of interesting possibilities 🙂

      Liked by 2 people

  5. Let me see if I’ve got this down correctly. We have 1n from the egg. That becomes 2n when the sperm fertilizes the egg. This changes the egg membrane to attract the tritiya/sperm combination, but when it joins the egg only the tritiya cell DNA is added. After this another egg that has just undergone the same process merges with the first egg, bringing us to a 6n giant cell that divides down to 3 2n cells (and possibly a DNA-less ghost cell).

    Does this mean that when the sperm and tritiya cell meet the tritiya cell basically cannibalizes the sperm? That would mean the tritiya cells have tentacle-like extensions and eat their fellow gametes. Many amoebas and most sperm cells are also grayish under a microscope. How long will it be before someone relaxes with the new gender enough to make jokes about ‘s itty-bitty funtime hollows?

    Liked by 2 people

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