🇩🇪 Deutsche Version: Mitomeiose

Note: The ethical judgments on this page refer exclusively to the action — never to the person who performs it or who came into existence through it. Every child conceived by this procedure is a complete human person with full dignity from fertilization onward. Cf. Note on Ethical Judgments.

Mitomeiosis is an experimental procedure intended to obtain a fertilizable egg from a body cell. The nucleus of a skin fibroblast is transferred into an enucleated donor oocyte, forced there into a premature reductional division, and the resulting haploid set is then fertilized with sperm. The name states the procedure exactly: mechanically a mitosis, in its result a meiosis.

It was presented in September 2025 by a research group at Oregon Health & Science University.

Ontological classification

is subclass of: somatic cell nuclear transfer (SCNT)
is subclass of: in vitro gametogenesis (in vitro oogenesis)
presupposes: artificial fertilization
presupposes: egg donation — the procedure is constitutively dependent on a third woman’s oocyte
produces: supernumerary embryos
is not: reproductive cloning — the nuclear genome produced is precisely not identical to another

The underlying problem

A mature oocyte carries 23 chromosomes, a skin cell 46. Together with the sperm’s chromosome set this would yield a triploid embryo, which is not viable. In nature the halving is performed by meiosis, and it accomplishes three things at once: the homologous chromosomes find one another and are paired, they exchange segments by crossing over, and because they are paired exactly one of each pair travels to each pole. The result is a complete set, not merely a numerically halved one.

Precisely this programme lies in the germline and is skipped by nuclear transfer. Mitomeiosis is the attempt to force the skipped step retrospectively.

The procedure

Enucleation. The spindle-chromosome complex is removed from a donated oocyte arrested in metaphase II. What remains is the cytoplasm with its maternal factors and the donor’s mitochondria.
Nuclear transfer. The nucleus of a skin fibroblast is inserted, in its unreplicated state — otherwise there would be nothing to halve, only sister chromatids to separate.
Sperm injection — without effect. Here lay the actual technical obstacle: adding sperm alone did not trigger the division, and the cells remained arrested in metaphase.
Activation. Only electroporation combined with roscovitine, a selective inhibitor of cyclin-dependent kinases, broke the arrest.
Forced reductional division and fertilization — in one stroke. The somatic chromosomes then separated, one set was extruded into a polar body, and the remaining halved set lay immediately as a zygotic pronucleus beside that of the sperm.

The order matters more than it appears: the sperm is already inside the cell when the halving takes place. A state of “halved but not yet fertilized” does not occur in the procedure — a point to which the question of status returns below.

Genetically such an embryo has three contributors: the skin-cell donor, the sperm donor, and the oocyte donor from whom the mitochondria derive — structurally the same constellation as in mitochondrial replacement therapy (three-parent IVF).

Why the procedure does not work

The decisive finding of the study is that the separation of homologous chromosomes occurred randomly and without crossing over — with a single documented exception at chromosome 8, which showed a preferential distribution. Without pairing there is no mechanism dividing a pair between the two poles; each chromosome decides independently. On average 23 chromosomes did indeed remain — but “on average 23” precisely does not mean “one of each chromosome.”

Here lies the conceptual point: euploidy is a statement about composition, not about number. A cell with exactly 23 chromosomes can be severely aneuploid if among them are two copies of one and none of another. Under purely random distribution the probability of a balanced set is on the order of one in a million. The study used 270 mature oocytes in total and produced 155 research embryos from them; in the fertilization experiment 82 SCNT oocytes were injected with sperm. The blastocyst rate was 8.8 per cent against 59 per cent in the controls, and all embryos analysed showed chromosomal imbalances.

Important for the classification: this is not a translation gap. With reprogramming it was: that worked in sheep in 1996, and it took until 2013 to make it work in humans. Ordered segregation following an artificially forced reductional division has so far succeeded in no species. What is outstanding is not adaptation to humans but the mechanism as such.

The imprinting problem

The second difficulty concerns genomic imprinting and is usually described too coarsely. A body cell is not free of imprints — it carries a complete and correct pattern at every imprinted locus, having inherited it from both parents. This is precisely why classical cloning works at all.

Mitomeiosis destroys this symmetry. It retains only one allele per locus, at random with respect to grandparental origin. If at a maternally imprinted locus the grandpaternal allele is retained, it meets the paternal imprint of the sperm: two paternally imprinted alleles, none maternal. Functionally this corresponds to uniparental disomy — the same constellation underlying Angelman, Prader-Willi, Beckwith-Wiedemann, and Silver-Russell syndromes.

The open status — but of which state?

The question of status is real, but it sits earlier than the obvious description suggests. Two states must be distinguished that are easily treated as one.

Before reduction. After nuclear transfer, a diploid somatic nucleus lies in the cytoplasm of the enucleated donor oocyte. Up to this point the procedure is step for step identical with the classical cloning procedure; the construction is materially the same. Whether a cloned embryo or a functional oocyte comes of it is decided only by what the operator does next — merely activate, or force the reductional division. An entity whose kind is determined by a technical choice still outstanding is precisely the case in which classification is decision and not finding. Here the question is open, and here the tutioristic principle in dubio pro persona applies — personal-ontologically the same situation as with the synthetic embryo model. The doubt is person-relevant because the same material constellation is uncontestedly treated as a candidate embryo on the cloning path: it would be arbitrary to record the same state now as a candidate for status and now as mere material, depending on the agent’s later intention.

After reduction. The halved state is haploid, not totipotent, has no developmental programme of its own and no trajectory other than fusion. It has neither arisen through fertilization nor emerged from the germline — both customary criteria fail to apply, and to that extent it remains open what it is to be classified as. But that it is no gamete in the ordinary sense — no germline origin, no recombination, a randomly halved somatic set — makes it a poor gamete, not a candidate for personhood. Two candidacies remain, gamete and mere artefact without natural purpose, and both lie below the threshold of personhood. Taxonomic indeterminacy is not person-relevant doubt (further under Ontologically Uncertain Status). If the tutioristic principle is extended to this as well, it becomes boundless and loses its force precisely where the candidacy is real.

This is expressly not a denial. What is said is not that no person is present here, but that no positive candidacy for one exists. The difference is not rhetorical: were absent totipotency to count as a sufficient ground for denying personhood, that would adopt exactly the functionalist criterion against which personal ontology otherwise argues — an actually absent capacity would decide about the nature. The same criterion would then also be available against developmentally impaired embryos.

A finding about the protocol. To treat the halved state as an entity of its own moreover presupposes a window of time the procedure does not have. The sperm had already been injected at the moment of activation, and the division thus triggered yielded a zygotic pronucleus immediately. Reduction and fertilization coincide. The halved state is a distinguishable step in the description of the process, not one isolable in the laboratory.

It remains notable that the scholarly literature does not pose the prior question. The older debate about naming the nuclear-transfer product begins throughout with the activated product as a candidate embryo. The state before the switch is thrown — the only one in which the question is still genuinely open — is treated by no one. Discussion of the procedure is conducted exclusively as a safety and efficiency debate: aneuploidy rates, blastocyst yields, timelines.

Toward the later stage the boundary is by contrast clear: the entities arising after fertilization are embryos in the full sense and persons with full ontological dignity.

Ethical assessment

The line of justification begins with ontological dignity: it is the sufficient ground of the Personalist Norm — the person is to be affirmed and loved for her own sake. The norm is violated by instrumentalization and by oblivion of the person. What must be examined is therefore at which points this procedure touches persons.

What does not carry here. The verdict does not follow from mitomeiosis being a nuclear transfer. A nuclear transfer is in itself an action upon cells, not upon persons. Nor does it follow from the prohibition of cloning: what is produced is no genetically identical human being but one from a random half plus a sperm’s chromosome set. Whoever drew the judgment from there would be borrowing a condemnation whose ground is here absent.

First point: the donor. After hormonal stimulation, tissue is removed from her whose personal share — her nuclear genome — is deliberately erased. What is used is not her contribution as a mother but her cell as a reaction vessel. Because her genetic share shrinks to the mitochondria, she simultaneously disappears from the description of a procedure of which she remains a necessary condition. That is instrumentalization and oblivion of the person at once (further under oocyte).

Second point: the embryos produced. They are persons in the First Dimension with a full right to life. The procedure produces them by design in numbers that presuppose the consumption of the majority, and it produces them in the knowledge of near-total aneuploidy — hence with the practical certainty that they are not viable. By the fontes moralitatis the object of the action determines its moral species. The object here is the bringing forth of persons whose failure is factored in. That is an intrinsically evil act; the intention of one day treating infertility changes nothing.

Third point: the construct before reduction. Here — and only here — it is precisely undecided whether a person is present. For just this the ontology has the precautionary principle: where the question of fact is open and the consequences of a wrong decision would be irreversible, the safer course is to be chosen. In dubio pro persona is no addendum but follows from the norm itself — whoever treats a person as a non-person violates her; whoever treats a non-person as a person loses nothing the norm protects. The argument is the asymmetry of the costs of error. It is not new: it matches the structure of the classical hunter’s argument (one who hears a rustling in the bushes does not shoot) and is conducted in the status debate as the precautionary argument; Dignitas personae 30 formulates it magisterially with reference to Evangelium vitae 60.

What follows. The assessment is unambiguous, but its grounds are distributed across points and are not interchangeable. Were the egg donation to fall away, the consumption of embryos would remain. Were the consumption of embryos to fall away, the open question of status would remain. Only the appeal to the prohibition of cloning would fall away without replacement — it was never a ground.

Corroboration, as confirmation and not as ground of the judgment: Donum vitae II,A,2 on recourse to the gametes of a third person; Dignitas personae 30 expressly applies the precautionary argument to cases of unresolved status; the Pontifical Academy for Life formulated in 1997 the point here treated under oblivion of the person, concerning the reduction of women to their biological functions.

What the procedure actually delivers

The balance is narrower than reporting suggests. The intended father’s genome is no achievement of the procedure — it arrives via sperm, and with ordinary egg donation the father is genetically related as well. The entire apparatus exists for the maternal half alone. Even that achievement is limited: the mitochondria still come from the donor, and because no recombination occurs the intended mother passes on intact grandparental chromosomes rather than reshuffled ones.

What is not delivered: safety, efficiency, anything bearing on the course of pregnancy. The procedure treats no disease and removes no infertility — the woman concerned also has a child with egg donation, and carries it herself. What changes is solely whose nuclear genome the child carries.

The strongest objection to this classification

It would be too quick to dismiss the whole as effort expended on a mere wish. The same argument would strike reproductive medicine as a whole: were genetic parenthood a mere desire, adoption would be the answer in every case. There is also a specific asymmetry — with egg donation the father within the couple is genetically related and the mother is not, and those affected describe this inequality as a burden in its own right, not as vanity.

Nor is the comparison with the alternative unambiguous. The competing route via stem cells requires rebuilding the entire female germline in the laboratory; in humans this has never succeeded. Nuclear transfer skips all of it by borrowing a finished oocyte whose cytoplasm is no approximation but the genuine product of follicular maturation. One should only see what this defence presupposes: that of all things the problem nuclear transfer creates for itself is easier to solve than the one the other route does not have.

Legal situation

In Germany the procedure would be impermissible on two mutually independent grounds: fertilizing an egg for any purpose other than bringing about a pregnancy in the woman from whom it came is a criminal offence, and so is egg donation itself. What is notable is what does not apply. The prohibition of cloning presupposes that an embryo arises with the same genetic information as another — which is not the case here. The prohibition on altering germline cells presupposes that a germline cell is affected — and by the statutory definition a skin cell is not. The same holds for the European prohibition of cloning, which expressly turns on the same nuclear gene set.

This is an example of technical development undercutting provisions tailored to a different procedure. Worldwide there is no explicit regulation of in vitro gametogenesis; in the United States there is neither a federal prohibition nor, in the state concerned, state law. What does apply there is a funding restriction — and that precisely does not prohibit the action, only the use of certain public funds.

Was den Menschen zum Menschen macht

Übersicht

Mitomeiosis