[chris (OP)]

We were talking today about paternity tests and whether a pair of identical twins could be discriminated as the father of a child.

I said no they could not, unless one of them had a new mutation detectable somewhere that was passed to the offspring and could thus prove parentage.

What does everyone else think?

[RD]

Apparently if their entire genomes are sequenced it could be determined who's the daddy ...

Gradl and his team took samples from a pair of male twins and looked at the entire three-billion-letter sequence, and they found a few dozen differences in their DNA.
The scientists also tested the son of one of the men, and found he had inherited five of the mutations from his father.
Having analysed the results, they are confident that they can now tell any twin from another, and from their children.

https://www.bbc.co.uk/news/magazine-25371014

[chris (OP)]

This was in-line with the answer I gave, although it's nice now to have that reference; thanks @RD

[chris (OP)]

Quite funny - when I look at this thread on paternity testing I've got adverts popping up on my screen for the world's worst airline - virgin

[syhprum]

Try Ryanair Virgin will look like Emirates in comparison.

[wolfekeeper]

I wonder if epigenetics might be employed- presumably the child's epigenetics would match the father's better than the twin's.

[RD]

This was in-line with the answer I gave, although it's nice now to have that reference ...

Here's a link the paper referenced in the BBC article ...

Finding the needle in the haystack: Differentiating “identical” twins in paternity testing and forensics by ultra-deep next generation sequencing. 

Monozygotic (MZ) twins are considered being genetically identical, therefore they cannot be differentiated using standard forensic DNA testing. Here we describe how identification of extremely rare mutations by ultra-deep next generation sequencing can solve such cases. We sequenced DNA from sperm samples of two twins and from a blood sample of the child of one twin. Bioinformatics analysis revealed five single nucleotide polymorphisms (SNPs) present in the twin father and the child, but not in the twin uncle. The SNPs were confirmed by classical Sanger sequencing. Our results give experimental evidence for the hypothesis that rare mutations will occur early after the human blastocyst has split into two, the origin of twins, and that such mutations will be carried on into somatic tissue and the germline. The method provides a solution to solve paternity and forensic cases involving monozygotic twins as alleged fathers or originators of DNA traces.

https://www.sciencedirect.com/science/article/pii/S1872497313002275

I'd want to see it being replicated, (rather than just one pair of twins), before being confident paternity in all cases can be established.

The cost of full genome sequencing has plummeted in the last decade, so it's now a feasible option ...
https://en.wikipedia.org/wiki/%241%2C000_genome#Commercial_efforts

[chris (OP)]

I wonder if epigenetics might be employed- presumably the child's epigenetics would match the father's better than the twin's.

Most of it gets reset by the chemical environment of the egg; but there are some parent-specific marks; it's an interesting point which I shall have to delve into a bit more deeply.

[evan_au]

The method they used would not work for identical sisters...
But maternity is more obvious than paternity...