There are three obvious ways where a <surprise> non-paternity is revealed
a) where you are adopted and your legal parents never told you that you were discovered under a gooseberry bush
b) where your Mum kicked over the traces with a chap with whom she wasn't living
c) where, with or without the knowledge of her partner, your Mum went for a spoonful of lovin' at a clinic - insemination by donor.
d) mix-ups with the wrist-bands in the maternity units do happen - but mostly in films
I went into the third c) category in a little detail recently when I heard that Berthold Wiesner had been liberal / flaithulach with his precious bodily fluids from 1944-1964. There I expressed the notion that it wouldn't worry me none if there was a DNA skeleton in our family closet. We already know that my great-grandfather was "a cook's bastard". If another skeleton, with more genes in common, materialised it wouldn't affect who I am.
But that's me, with blunted affect and at least a few steps along the spectrum. Other people are much more invested in their genetic relatives, presumably because they have taken up a contrary position in the nature vs nurture wars. A recent HuffPo story peels back the story on a couple of pally (but unrelated) thirty-somethings who sent some spittle into 23andMe / ancestry.com / myheritage without really thinking through the consequences of discovering whose sperm engendered them. HuffPo is quite huffy about the irresponsibility of people who spend their $100 on DNA analysis for a bit of a larf. The default is that your DNA becomes the company's DNA unless you explicitly try to get the genii back in the jam-jar. Therefore by extension, your family's DNA is then Out There, to be (potentially) battened onto by drug companies seeking the grail of personalised medicine or by a parcel of needy and indigent blood-relations.
HuffPo also dig a little into the competing rights to privacy / disclosure for the parents and offspring. Usually, if there is discordance in what's wanted, it's the offspring who wants a relationship with a biological parent and the parent who has moved on to other relationships and may not want youthful indiscretions to come rattling out of the closet. Almost by definition, at least 20 years will have passed since the fateful fetal meeting of sperm and egg. We've recently had a referendum which said that zygotes (as we biologists call fertilised eggs) and embryos do not have an automatic right to life. But if a pregnancy has gone to term, I think (for now - convince me otherwise) that person has a right to know who their parents are which out-bids any parental right to privacy; however inconvenient or traumatic the appearance of a child-of-loins may be. Especially that applies to the the male parent - whose biological contribution can be weighed in a very small receptacle and so should be made responsible for the consequences of that contribution.
On the wireless a couple of weeks ago we had Catherine Zappone, minister of children, talking about the provisions of the Adoption and Information Tracing Bill which is wandering through the legislative process. She hopes to authorise (and resource!) Tusla - the child and family agency - to consult the records and act as an honest broker between the competing claims of the two generations. Honest yes but efficient and/or tenacious maybe not so much. And the state will be required to divert tax dollars towards servicing this new service. The advocates for the 'bio-orphans' are trying to tease apart privacy and secrecy: with shame embedded in Irish culture it's probably not a good idea to publish DNA parents like we publish tax-defaulters - the neighbours don't need any more salacious gossip-fodder. On the other hand, we don't want blokes hiding behind a cloak of secrecy to evade responsibility. And could we all be a bit more careful when it comes to sex? After all "The pleasure is momentary, the position ridiculous and the expense damnable" . . . and the responsibility onerous - I put it in quotes but it's not from Lord Chesterfield.