I briefly covered the warning to expect surprises in this blog post, DNA and Family Tree Research: Goodbye NPE, Hello SDS – some causes of Surname or…, but I think it needs its own post as it’s something that comes up often enough where somebody finds out they have half or full siblings they weren’t aware of, or Dad, Mom, or both aren’t their biological parents. As I mention in the above post, I prefer NPE (Not the Parent/s Expected as opposed to Non-Paternity/Paternal Event) over other choices. Misattributed Parentage Event (MPE) would be my next choice since Non-Paternity/Paternal Event is clearly a case of “Who’s the Daddy” and it’s frequently a case where mother or both parents aren’t as expected. I would add don’t avoid taking a DNA test because you are trying to hide a known or suspected surprise as other family members may take do and reveal the surprise you aren’t wanting revealed.
One of the most common reasons some won’t DNA test is because they know, suspect, or have some inkling there is a family secret that DNA will blow the lid off. Guess what? It doesn’t matter if you refuse to DNA test since a close family member is probably at some point going to test which will make your decision to not test irrelevant. I tell people all the time – DNA makes keeping family secrets impossible. Better to come clean and be honest since I see too many willing to lie and include some of the lies/explanations below. Worth noting you don’t the truth and if a person gives you an explanation, it’s often not the real reason. For example, an affair where the wife says it was rape. In cases of rape or incest, she could have blocked it out and may be very unlikely to talk about it, much less admit it. It could be consensual (think Romeo and Juliet); also one parent (in rare cases, both parents) may not know – seen enough fathers who weren’t told the truth; in other cases, a baby switch could happen – stealing babies from hospitals happened enough that many hospitals now take steps to prevent it from happening. It could be a fertility clinic error (intentional or not, see Lisa’s story below). Maybe an adoption where the parents don’t tell the child; in some of these cases, the adoption wasn’t legal. In other cases, the mother lied on the birth certificate, with or without the knowledge and consent of the biological father or the man named as father on the record. There are a host of other reasons for a NPE showing up.
A story I often use is Lisa (a name I made up to protect the privacy of the family even though they have talked about it publicly) – Lisa’s parents had a family secret; it shouldn’t have changed the DNA results, but it did. The family secret was they couldn’t get pregnant the old fashioned way so they used a clinic to take Mom and Dad’s samples to make Baby Lisa and they never told her. She convinces them to do a DNA test for fun. Mom and Lisa – parent/child match. Dad/Lisa – not a match. That’s when they came clean about the clinic. Turns out the clinic had an employee who substituted his sample for Dad’s sample.
Some common excuses/explanations a person may be told by those trying to protect a family secret:
DNA is wrong (at close levels, like parent/child/sibling/half-sibling, it’s extremely unlikely to get it wrong; it may be off a bit from the expected norm)
Chimera effect – this is one of the most common reasons I hear, but rarely from experts. https://en.wikipedia.org/wiki/Chimera_(genetics)#Humans – worth noting that if it is a case of chimera effect, there would still be a relationship between the individuals, which may be a generation off (for example, mother showing as grandmother, aunt, etc.). How rare the condition is open for debate as some claim it’s very common and others say it’s very rare. There’s a good CSI episode (warning it involves rape: https://www.csifiles.com/reviews/miami/bloodlines.shtml); also check out: https://en.wikipedia.org/wiki/Genetic_chimerism_in_fiction
DNA Lab error: while this can happen, it’s pretty rare.
Refusing to test – another common one especially if a person believes or suspects NPE.
Swapping samples by a tester – this is usually done by either the tester or somebody acting with or without the tester’s knowledge. Most common reason is to avoid proving a relationship since some are so deep in denial, they would willingly use somebody else’s DNA to disprove the relationship. In this case, https://www.mirror.co.uk/news/uk-news/scheming-dad-sends-brother-take-7135315 the person was caught and in my opinion, got off easier than they should have. Important to understand – in some locations (some U.S. states and a few foreign countries), not being the biological father doesn’t affect issues like child support. If you were married to the mother when she got pregnant, you may be considered the father even if she admitted that you aren’t and the DNA backs it up.
Sperm and/or egg donation: I have a friend who found an unknown biological niece and in this instance, it was a case where his brother sold sperm to pay for medical school. The brother was promised (back in the 1970s and 1980s) anonymity. His brother hasn’t DNA tested, but the fact my friend tested shot down the anonymity.
Using different DNA testing companies – okay this one will be valid in some instances, but not valid in other cases; the following chart, https://isogg.org/wiki/Autosomal_SNP_comparison_chart, shows how many SNPs in common between the different companies and chip versions. This will apply more to GEDmatch including GEDmatch Genesis, DNA.Land, WeGene, FamilyTree DNA (aka FTDNA; if you do an autosomal transfer from another DNA company to FTDNA), MyHeritageDNA, and similar matching systems where you compare DNA results from different companies, you may find your matching to be slightly off as there can be sizeable differences in how many SNPs are in common. A quick look at the ISOGG link, shows you can have anywhere from 50K SNPs different to over 500K SNPs difference. The fewer SNPs in common, the higher the risk of missing relationships and getting wrong. For example, two siblings testing at different companies and comparing using any of the companies or websites I mentioned in this section could appear as half-siblings even though if they had tested at the same company with the same chip, they would show as full siblings.
Instead of trying to keep hiding what may or may turn out to be a family secret, how about coming clean? In one case, there was a suspected NPE, as the mother admitted cheating and had the husband believe their youngest child wasn’t his. He went to his grave believing this lie. Turns out another relative tested and their results proved the father was indeed the father.
If you have other examples, let me know and I will add them above (minus any identifying personal information).