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Would it theoretically be possible to select two sex cells after a male meiosis (filtering out the two where crossover had taken place) and combine each with two sex from a female meiosis (imagining they were all egg cells, even though only one would be) to create offspring with inverse inherited parental DNA of one another?

For example: If the mother's DNA is AB and father's is CD then the offspring could have AC and BD - inherited from both parents but completely different from one another.

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Theoretically? Yes. Very theoretically possible.

In practice? It's difficult to isolate the exact daughter cells (sperm) from the same meiotic event, have these cells complete maturation, and only then have them fertilize an egg. Normally you need quite a lot of sperm cells even with in vitro fertilization, but also in principle all you need would be a single sperm cell to make a zygote!

To address some misconception: when you say "inherited from both parents but completely different", that applies also for regular sex cells and fertilized eggs. You don't need to fish for the precise 2 daughter cells following meiosis to get this outcome. Mitosis produces 2 genetic copies, while meiosis in humans produces 4 unique daughter cells. All individuals, as diploid as we are as humans, are products of genomes that have been very well shuffled (recombined).

Reality: the real-life reasons to perform such a procedure would be taken as very dubious, so I don't think realistically anyone would perform this. But in the designer baby era of the future, who knows!

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  • $\begingroup$ Sure it would be bery dubious. Was just a silly idea i had. I did have a misconception about crossover where i thought only 2 daughter cells would recombine, when it seems they all do. Still, it seems the resulting children would have mutually exclusive DNA besides that which is shared by both parents. Would i be right in thinking that one child would recive an X chromosome and the other Y from the sperm making the children opposite sex too? $\endgroup$ Apr 12, 2021 at 13:44
  • $\begingroup$ Correct! The ratio of Y and X chromosomes in the haploid sex cells (spermatozoa) is 50:50 as a result of meiotic distribution, and this originates from the X and Y chromosomes being separated between two daughter cells during meiosis. $\endgroup$
    – S Pr
    Apr 12, 2021 at 14:09
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Here there be monsters

The biggest problem with your scenario as presented is that the complementary genes in the female do not go into the "secondary oocyte" but into the "first polar body" ("2" below).

enter image description here

The first polar body remains in the perivitelline space beside the oocyte, but it is a tiny thing, generally considered too small to potentially make a zygote. It is emitted as a diploid during the first division of meiosis, and divides again afterward. I think the one below has already divided.

Now, because it's impossible, we should naturally expect to find such a case, and I will not disappoint: Bieber, 1981. In that case the polar body had not divided yet, and the resulting twin, within the chorion, was a triploid and severely deformed "acardiac monster". A 2015 review mentions polar body twinning without describing the possibility of diploids, so I'll assume this hasn't actually been demonstrated. I know the first polar body is a bit half-hearted about its division.

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It should be relatively straightforward to obtain immature sperm while they are still linked by cytoplasmic bridges as illustrated above, do in vitro sperm maturation to obtain complementary sperm, and attempt some sort of fertilization of egg and a daughter of the first polar body. The resulting twins would share a chorion but monochorionic and diamniotic. Such a procedure would still be very likely to produce a malformed embryo due to the development of a very tiny zygote. I was concerned about epigenetic differences, but after a helpful comment, I did find a reference that the methylome is similar to that of the secondary oocyte, and a paper reporting that it is possible to transfer polar body nuclei to oocytes with 42% viability. Given remaining uncertainty and a lack of apparent medical necessity, it might still be more advisable to stick to routine human cloning with germline genetic modification. :)

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  • $\begingroup$ I knew there'd be a problem with female meiosis producing only one egg, but I guessed maybe DNA could maybe be transplanted from a polar body into another egg. I hadn't considered that epigenetic information could make this infeasible, so thanks for the additional information. $\endgroup$ Apr 12, 2021 at 19:57
  • $\begingroup$ You are right! I'd seen one thing about epigenetic changes and polar body extrusion which I may have misinterpreted, given other sources I found. I'll update the answer accordingly. $\endgroup$ Apr 12, 2021 at 23:10

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