Who the heck's my pop?

July 5, 2008 3:09 PM

How can I determine, with access to limited biological data, if my father is not who I thought he was?

I was recently shown a photograph of my mother's college boyfriend that gave me a shock: he looks uncannily like me, to the point that people shown the photo assume it is of me. My divorced mother is being cagey about the possibility that this man could be my biological father, and while approaching my potential biological father is something I'd be willing to do, I hesitate to contact him and stir up a beehive in his life if this is just a coincidence. And of course bringing this up with the man who raised me is out of the question.

So my query, to all you genetic scientists and hobbyists out there: with access to my own male DNA and that of my sister (who is almost certainly the child of my mother and the man who raised us), is it possible to determine if we have the same father? If the results of such a test existed to show that my sister and I do not share a father, I'd feel better about approaching my mom's ex-boyfriend.

If so, how would we go about testing for this without spending a fortune? Follow up questions can be sent to the anonymous address [e-mail] and I will respect your anonymity, too.

Thanks for helping me sort this wackiness out!

posted by anonymous to Health & Fitness (10 answers total)

Yes, you can definitely determine whether or not you and your sister share the same set of biological parents. What you want to look for is sibling DNA testing. There are numerous services available, all of which will set you back several hundred dollars. But testing your sister's DNA against your own will be a surefire way of determining the parents.
posted by phunniemee at 3:18 PM on July 5, 2008

An easy, but not surefire test that might yield an answer is blood type - if you know your mother's and sister's father's types, there are scenarios that would rule out that man being your biological father. For example, if both your mother and sister's father are any combination of types A and O, and you're B or AB, there's no way that man is your father.
posted by ripple at 5:04 PM on July 5, 2008

The way I wrote that might be a touch confusing -- by "that man" I'm referring to your sister's (putative) biological father, not your mother's college boyfriend.
posted by ripple at 5:06 PM on July 5, 2008

You can purchase over the counter paternity tests at some drug stores.
posted by whatisish at 5:30 PM on July 5, 2008

After re-reading your question, you probably would need a sample of either of the suspected daddy's DNA, so OTC paternity tests aren't likely your best bet.
posted by whatisish at 5:34 PM on July 5, 2008

Yes, you can definitely determine whether or not you and your sister share the same set of biological parents.

Note that doesn't tell you whether it's you, her, or perhaps both of you that have a different father to the one who raised you.
posted by rodgerd at 6:16 PM on July 5, 2008

Well, do you have access to the DNA of the father who raised you (used razor blade, comb with hair etc.)? If yes then a lab could do a test but I don't know if this would be legal in the US. An Uncle of you father would probably work too.

BTW, interesting story, would you mind posting how it turned out?
posted by yoyo_nyc at 7:04 PM on July 5, 2008 [1 favorite]

I had a D in 8th grade science, but the only thing that clicked was that the pale eye (blue, gray, green) gene is recessive. Two pale eyed parents do not EVER result in a brown eyed baby. Two brown eyed parents can have a pale eyed baby if they both carry the pale gene. The teacher told us that this is how one of his students found out that she was adopted.
posted by brujita at 12:40 PM on July 6, 2008

I have a cautionary tale of going by looks in a photograph in determining parentage or even second guessing parentage. My mother was adopted and curiously looked like the spitting image of one of her adopted aunts, and enough like a sister of that aunt to suspect somehow one of them was her biological mother. The confrontation that ensued (this was long before DNA testing) only served to completely sever what few ties there were remaining and created much animosity. Many years later, for health reasons only, we were able to finally see her original birth certificate. Her biological mother was someone we'd never heard. When a photo arrived of my mother's grandmother (mother's mother), we then truly discovered from where my mother inherited her looks, which turned out to be a completely different ethnic group than the adopted aunts!

Keep any speculation closely guarded and please proceed with caution. By all means, do investigate, but know that it might just be a wild goose chase and idle speculation may hurt people you love if it turns out to be baseless.
posted by kuppajava at 1:07 PM on July 6, 2008

Second on not going by looks. People cherish the idea that we can see likeness, but science has shown over and over again that we are just no good at it.

If you really want to know, though, and your divorced mother is being cagy for some reason... well, polymerase chain reaction testing has never been cheaper.
posted by Lesser Shrew at 6:55 PM on July 6, 2008