Researchers have produced mice with two maternal or two paternal sets of nuclear DNA. The nucleus is the part of a cell that holds most DNA. Birth, adult survival, and the ability to breed are distinct outcomes. The studies test different outcomes. Bimaternal and bipaternal mice get these names from the source of their genes. The terms do not describe parenting or social roles.
What is genomic imprinting?
Imprinting means a gene's activity can depend on which parent's copy it came from. Epigenetic marks, including DNA methylation, help control that activity (Li et al., 2018). When both copies have the same parental origin, needed marks may be missing or wrong. Imprinting does not rank one parent above the other.
What did the first bimaternal mouse study show?
In 2004, researchers used two maternal sets of genes, one from each egg cell. One egg was not yet growing; the other was fully grown. The work also used a change at the H19 region. One mouse reached adulthood and reproduced (Kono et al., 2004). These eggs had been changed in the lab. The result did not show that unchanged eggs could grow on their own. It was not a human clinical result.
What did the lifespan study find?
A 2010 study compared 13 engineered bimaternal mice with 13 controls. It targeted the Igf2-H19 and Dlk1-Gtl2 regions. The bimaternal mice lived a mean 186 days longer (Kawahara & Kono, 2010). The paper first appeared online in 2009. That figure is a mean difference in days within a small mouse study, not a percentage. It does not prove that paternal DNA always shortens life.
What did imprinting-region deletions show?
In 2018, three imprinting-region deletions produced fertile bimaternal mice. Seven deletions produced bipaternal pups that died soon after birth (Li et al., 2018). These results apply to those methods. They are not fixed limits on what later work could achieve.
What did the 2023 oocyte study show?
A 2023 study started with cells from male mouse tails. Researchers turned them into stem cells and changed their chromosomes from XY to XX. They then grew working oocytes, or egg cells, in the lab. These eggs gave rise to offspring after fertilization (Murakami et al., 2023). The method still needed eggs, sperm, and a female to carry the embryos.
What did the 2025 imprinting studies show?
A 2025 study modified 20 imprinted loci, which are DNA sites. Some bipaternal mice reached adulthood, but survival was low (Li et al., 2025). That is not proof of normal health, fertility, or human safety.
A separate June 2025 study edited DNA methylation at seven imprinting control regions. This changed epigenetic marks. Two sperm nuclei went into an egg whose own nucleus had been removed. Female mice carried the embryos. Of 259 transferred blastocysts, or early embryos, 3 became live pups. Two reached adulthood. Both adult males produced offspring with females (Wei et al., 2025).
Can one number of edits work for every protocol?
These studies do not establish one count. They changed different sites, used different kinds of edits, and started with different cells. They also tested different outcomes. Their edit counts cannot be read as steps in one method or as a shared minimum.
What do bimaternal and bipaternal mice studies show?
| Endpoint | What it shows | What it leaves open |
|---|---|---|
| Live birth | Pups survived to delivery | Adult health, fertility, reliability |
| Adulthood | Some animals survived to maturity | Normal health, lifespan, fertility |
| Fertility | At least one animal reproduced | Rates, health, human safety |
Each endpoint answers its own question. A mouse that reaches adulthood may not be healthy or able to breed. An animal that breeds does not prove the method is safe for all animals. Health and the ability to breed need their own checks.
How should you read a new headline?
A headline tells you the result someone chose to highlight. To weigh that result, turn to the study itself. These five checks will help you decide what a mouse claim about two mothers or two fathers actually shows.
- Check the exact paper and method. Find the original study and read the methods section. The claim may describe a method, not a result.
- Check what was measured as the outcome. Look for the specific test used, not the word chosen in the headline.
- Check the denominator and stage. Note how many attempts started and where losses occurred.
- Check whether the surviving animal shows the full method worked. One animal reaching an endpoint does not prove the whole process is reliable.
- Check the scope. A mouse result informs mouse biology. It does not establish safety, fertility, or clinical use in people.
Take a hypothetical claim: "Mice with two fathers reached adulthood." Four questions would sharpen it.
How many attempts did it take? Look for the full flow of cells, embryos, and transfers, not just the number of survivors. Which animals were tested for fertility? Offspring tests answer that; adult size does not. What health checks followed? Look for actual follow-up tests, not a photograph. Which exact method produced the result? A result from one method need not hold for another. Nor can it be assigned to an older or later study.
If a result is not reported, you cannot infer it failed. Missing data means "not shown," not zero. The paper may simply not have tested it, or may not have published it. Treat absent information as a gap in evidence, not as a negative finding.
Denominators matter. Survival among live pups asks a different question from success among all transferred embryos. Both can be useful, but neither answers the other. A small, selected group of survivors also says little about the health of every attempt. If the group was chosen because those animals lived, their outcome is not a fair sample of the whole effort.
The claim can be real and still narrow. Ask what was shown, in how many animals, at which stage, and under which method. That keeps a striking headline in proportion.
Next in this series: Life history trade-offs. Browse the full Insights library.
Key takeaways
- The terms describe the source of nuclear DNA. They do not describe social family roles.
- Birth, adulthood, and fertility are separate endpoints, and each study reports different ones.
- The studies do not establish a shared edit count. Methods, sites, and starting cells all differ.
- The work is engineered mouse research. It does not show human clinical readiness.
Frequently asked questions
References
Kono, T., Obata, Y., Wu, Q., Niwa, K., Ono, Y., Yamamoto, Y., Park, E. S., Seo, J. S., & Ogawa, H. (2004). Birth of parthenogenetic mice that can develop to adulthood. Nature, 428(6985), 860-4. doi:10.1038/nature02402
Kawahara, M., & Kono, T. (2010). Longevity in mice without a father. Human Reproduction, 25(2), 457-61. doi:10.1093/humrep/dep400
Li, Z. K., Wang, L. Y., Wang, L. B., Feng, G. H., Yuan, X. W., Liu, C., Xu, K., Li, Y. H., Wan, H. F., Zhang, Y., Li, Y. F., Li, X., Li, W., Zhou, Q., & Hu, B. Y. (2018). Generation of Bimaternal and Bipaternal Mice from Hypomethylated Haploid ESCs with Imprinting Region Deletions. Cell Stem Cell, 23(5), 665-676.e4. doi:10.1016/j.stem.2018.09.004
Murakami, K., Hamazaki, N., Hamada, N., Nagamatsu, G., Okamoto, I., Ohta, H., Nosaka, Y., Ishikura, Y., Kitajima, T. S., Semba, Y., Kunisaki, Y., Arai, F., Akashi, K., Saitou, M., Kato, K., & Hayashi, K. (2023). Generation of functional oocytes from male mice in vitro. Nature, 615(7954), 900-906. doi:10.1038/s41586-023-05834-x
Li, Z. K., Wang, L. B., Wang, L. Y., Sun, X. H., Ren, Z. H., Ma, S. N., Zhao, Y. L., Liu, C., Feng, G. H., Liu, T., Pan, T. S., Shan, Q. T., Xu, K., Luo, G. Z., Zhou, Q., & Li, W. (2025). Adult bi-paternal offspring generated through direct modification of imprinted genes in mammals. Cell Stem Cell, 32(3), 361-374.e6. doi:10.1016/j.stem.2025.01.005
Wei, Y., Yue, T., Wang, Y., & Yang, Y. (2025). Fertile androgenetic mice generated by targeted epigenetic editing of imprinting control regions. Proceedings of the National Academy of Sciences, 122(27), e2425307122. doi:10.1073/pnas.2425307122
This article is for informational and educational purposes only and does not constitute financial, legal, tax, medical, or professional advice. Individual results vary.