There is no perfect genetic tell.
In poker, a tell is something you do that gives away the fact that you’re bluffing. Maybe you itch your nose every time you have a bad hand. So now when you make a big bet and itch your nose, you’ll lose to the players who have caught on. Your nose itching is your tell.
In an article about the 4 percent of men who are raising someone else’s kid, Men’s Health lists what it calls genetic tells. Instead of nose itching, these tells are traits to look for in a child who might not be yours. The idea is that in a simple genetic world, some traits are impossible for certain parents to pass on. So dad is supposed to use these traits as a tell to uncover mom’s bluff about paternity.
The problem, though, is that none of these traits are a sure way to exclude paternity. In fact, most of the traits they list can be safely ignored. Light haired parents can and do have darker haired children. Parents without a cleft chin can have a child with one. Parents with attached earlobes have kids with unattached ones. And tongue rolling seems to hardly be genetic at all.
All of these exceptions are actually pretty common. The one trait they discuss that has some validity is blood type and even this one isn’t bulletproof. For example, in Japan, an AB man had an AB child with an O wife, which conventional genetics says is impossible. But the dad really was the dad. To understand how this happened, we’ll need to quickly go over blood type.
There are three versions of the ABO gene — A, B, and O. All of the blood types come from mixing and matching any two of these versions. Normally, we pass just one version of each of our genes to our kids. So an AB parent can usually pass only an A or a B, not both. And an O parent can only pass O — she or he has two O versions. So only A or B children should be possible.
What happened in our exception was that the dad’s DNA changed so that his A and B versions fused together. His sperm now contains either AB or O so that he will have an AB child with an O wife half the time. And the equally “impossible” O child the rest of the time.
I don’t want you to think this sort of thing is common with blood type. It isn’t. But these kinds of exceptions do happen.
And with the other tells they happen a lot. It is pretty common, for example, for tongue rolling to not follow any particular pattern in a family. Many people can even learn to do it! So if your son can roll his tongue and you and your spouse can’t, it is nothing to worry about. Tongue rolling is a terrible genetic tell.
Remember too that even a tell in poker is not absolute. Maybe the player just happened to itch her nose a couple of times during the game and they happened to be when she had a bad hand. Now when you try to use the information about her tell against her, it doesn’t work. You lose. Just like your own child might lose if you take these traits too seriously.
Academic article about parental discrepancy:
Dr. Barry Starr is a Geneticist-in-Residence at The Tech Museum of Innovation in San Jose, CA.