Is it possible to determine who of the two identical twin brothers is a father?

[Eugene Finkelstein]

Hi All!
First of all, I'm interested not in a hypothetical info, but in practical abilities based on the modern level of technological advancement - were there any precedents of such determination as for now?
Secondly, I'll describe situation. Imagine there are two brothers. They are identical, or monozygotic, twins. Both of them were sexually active with one female during one night and one year later this girl came to them and said: "Hey, boys! Look, it's a son... of you, yes. And now some of you should pay aliments. Thank you for understanding, honeys".
The standard paternity test did recognize - yes, this boy is a son of... one of them. But could not determine, what brother is accidentally guilty more than other one, and who exactly should pay the aliments for raising a child.
So, are there technologies in modern genomics today that can determine - who'd became a sponsor for the next 18 years?

[Eugene Finkelstein]

As there are no replies, I'll up the topic for one time & will also try to do my personal research with providing an adequate answer (tomorrow or in few days). Although, you should notice, I'm not the person in good relationships with modern science, so this near-future answer may be not in touch with all the recent advancements in genomics, specifically in the forensic/judicial subfield of it. Anyway, will do my best. Thanks for understanding.

[Colonel Frank Grimes]

The answer is no.

[Eugene Finkelstein]

Not sure about that, since there are mutations since zygota twinning, so "identical twins" aren't completely so - those differences may be harder to identify and few, I guess, but it's the start point to consider. I'll look for scientific works soon.

[Sylvanas]

With standard tests, no. Maybe with WGS, but you can't be 100% sure...

[kingmob]

Probably not with absolute certainty.

[Seya]

I don't see how possible...They have identical genes.

[kingmob]

To understand the process of the monozygotic twins (my sons are such), the second twin splits out of the first at some point in the first weeks.

They are essentially the same person biologically in every way.

Another little tidbit to blow your mind, let's say the twins marry and have children of their own. Those children are going to be half-siblings between them (25% DNA) and not cousins (12.5% DNA) like normal.

[Eugene Finkelstein]

Those children are going to be siblings between them (50% DNA) and not cousins (12.5% DNA) like normal.

... and, making your point even further, the children of two married sets of monozygotic twins would be essentially brothers and sisters, so full siblings.

[Petalpusher]

Interesting question, honestly i don't know but im inclined to believe it's possible, not with a regular test.


Found this as i looked up


Paternity Testing in Identical Twins
Typically when there is a question of paternity, you take a specific test that compares 15 to 20 pieces of DNA between the potential father(s) and child. Check out this article to learn more about how paternity tests work.

But given you’re looking for a few differences in billions of letters, it’s pretty unlikely a standard paternity test can distinguish between identical twins.

A few years ago, this would have been the best you could do. But it’s possible now to read all the DNA in a person, in a fairly cost-effective way. We call this type of testing Whole Genome Sequencing (WGS). When you do this, in theory you should be able to identify small letter changes that exist in one twin but not the other.

One research group used this kind of technique to study a pair of twins and a biological child to one of these twins. They were able to successfully identify the true father of the child.1 But it’s still unclear how often this technique will be able to give a clear answer.

More recently, some companies are allowing their consumers to order this type of whole genome testing. But keep in mind genetic testing isn’t perfect – and sometimes reveals unexpected things.

https://www.thetech.org/ask-a-geneticist/paternity-and-identical-twins#:~:text=Identical%20twins%20have%2C%20for%20 the,able%20to%20answer%20this%20question.

[Jehan]

It's possible that identical twins doesn't share the exact same adn but the difference is tiny. I doubt the parternity test who can be bought by the public would detect it. But the police acheive to do the difference.

[Mopi Licinius Crassus]

I don't see how possible...They have identical genes.

my identical twin brother has 2 sons

i take it genetically they are my sons too :p

[Kriptc06]

No, they are identical

[Eugene Finkelstein]

From my quick read (only "abstracts" and "conclusions"), the summary:
Yes, it can be done in most if not all, cases using the WGS technique. Although there are currently only a dozen of practically solved cases in paternity disputes and forensic investigations, they proved to be a success.
Quote: ... arising from a single fertilization event, MZ twins nevertheless continue to acquire somatic mutations during their development, including those that occur in the germline. Provided that paternity had been narrowed down to the twin pair beforehand by classical DNA analysis, one post-zygotic mutation would suffice to assign the paternal compartment of an offspring genome unambiguously to either twin if that mutation is found in the offspring and one twin, but not in the other twin.
Reading:
1. Krawczak, M., Cooper, D. N., Fändrich, F., Engel, W., & Schmidtke, J. (2012). How to distinguish genetically between an alleged father and his monozygotic twin: a thought experiment. Forensic Science International: Genetics, 6(5), e129-e130.
2. Weber-Lehmann, J., Schilling, E., Gradl, G., Richter, D. C., Wiehler, J., & Rolf, B. (2014). Finding the needle in the haystack: differentiating “identical” twins in paternity testing and forensics by ultra-deep next generation sequencing. Forensic Science International: Genetics, 9, 42-46.
3. Krawczak, M., Budowle, B., Weber-Lehmann, J., & Rolf, B. (2018). Distinguishing genetically between the germlines of male monozygotic twins. PLoS Genetics, 14(12), e1007756.
4. Yuan, L., Chen, X., Liu, Z., Liu, Q., Song, A., Bao, G., ... & Wu, Y. (2020). Identification of the perpetrator among identical twins using next-generation sequencing technology: A case report. Forensic Science International: Genetics, 44, 102167.
5. Turrina, S., Bortoletto, E., Giannini, G., & De Leo, D. (2021). Monozygotic twins: Identical or distinguishable for science and law?. Medicine, Science and the Law, 61(1_suppl), 62-66.
6. Rolf, B., & Krawczak, M. (2021). The germlines of male monozygotic (MZ) twins: Very similar, but not identical. Forensic Science International: Genetics, 50, 102408.
7. Butler, J. M. (2023). Recent advances in forensic biology and forensic DNA typing: INTERPOL review 2019–2022. Forensic Science International: Synergy, 6, 100311

[Monapps]

Only in extremely rare cases where mutations affect germ cells.

[Lemminkäinen]

It is possible if you have good luck. Everyone has random mutations, also identical twins. Statistical analysis would find them, but you need perhaps a full genome scan. If you are male, then it is possible that only Y-chromosome is needed to scan, but it would be like a jackpot to get that mutation.

[Eugene Finkelstein]

One additional work, very new & summarizing in nature of all previous studies, also with some perspectives on future development of the issue:
Hwa, H. L., Lin, C. Y., Yu, Y. J., Linacre, A., & Lee, J. C. I. (2024). DNA identification of monozygotic twins. Forensic Science International: Genetics, 69, 102998.