# DNA Testing for the common citizen?
**URL:** https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494
**Category:** Factual Questions
**Created:** [March 4, 2004, 1:01pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494 "2004-03-04T13:01:58Z")
**Posts on this page:** 6
**Page:** 1
### Author:  [@Jinx](https://boards.straightdope.com/u/Jinx)
#### Post date: [March 4, 2004, 1:01pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/1 "2004-03-04T13:01:58Z")
Many SDopers may have heard that too-wild to be true story from Philly of a mother burned out of her home about 5-6 years ago and “losing” her infant daughter…suddenly is at a birthday party very recently and sees a girl who she is convinced IS her long-lost daughter. So, she tricks the girl into allowing her to cut a sample of her hair (by claiming there was gum in her hair) and she gets a DNA test done which (allegedly) proves it’s her daughter.
Now, just how easy is it to get a DNA test done? How costly? How thorough? (I imagine they might only test for only specific things for which you have paid for.) Also, if the girl were actually the daughter of a sister, or another child of the same biological father…aren’t the odds against a 100% confirmation? The matching evidence might be just statistically high enough to suggest a confirmation, but the conclusion might be wrong. (I understand they break the DNA moelcule into several fragments and count the matches within each fragment.)
What do you know about DNA testing and its validity under such circumstances?
- Jinx
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### Author:  [@dylan\_73](https://boards.straightdope.com/u/dylan_73)
#### Post date: [March 4, 2004, 1:45pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/2 "2004-03-04T13:45:56Z")
I’m afraid I don’t know, but you reminded me of the [Discovery DNA Explorer Kit!](http://shopping.discovery.com/stores/servlet/ProductDisplay?catalogId=10000&storeId=10000&productId=53965&langId=-1&search=Y&searchKey=-471832413)
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### Author:  [@zimaane](https://boards.straightdope.com/u/zimaane)
#### Post date: [March 4, 2004, 3:32pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/3 "2004-03-04T15:32:17Z")
Ordinary people can have their DNA tested to determine family relationships easily. When my mother-in-law applied for a visa to visit the US, she and my wife were tested to insure that they were genuinely mother and daughter. My wife went to a small office in a medical park and had blood drawn, and my m-i-l did the same abroad. The results were unambiguous. It is also pretty common in cases of disputed paternity for people to arrange for DNA testing.
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### Author:  [@js\_africanus](https://boards.straightdope.com/u/js_africanus)
#### Post date: [March 4, 2004, 4:21pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/4 "2004-03-04T16:21:11Z")
> [@Jinx](#):
>
> What do you know about DNA testing and its validity under such circumstances?
>
> - Jinx
As far as I am aware, there has been only _one_ blind test of DNA testing and it found false positives for one out of one-hundred cases. In other words, if there is a rape in a city of 1 million men, you would expect to see ten-thousand men test positive for the rape sample. It is one tool that can be very useful, but it is way too abused by law enforcement & the public. To put another way, it is so badly abused that a specific type of false reasoning, the Prosecutor’s Fallacy, goes part and parcel with DNA evidence.
I am quite curious whether there was an independent, double-blind test of the child’s DNA relative to the “parent”. (I haven’t read any stories on it.) I hope everything is being done properly.
A good book to read that will be much more informative about this is Gerd Gigerenzer’s _Calculated Risks_. I strongly recommend it.
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### Author:  [@sevenwood](https://boards.straightdope.com/u/sevenwood)
#### Post date: [March 4, 2004, 7:02pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/5 "2004-03-04T19:02:45Z")
> [@Jinx](#):
>
> So, she tricks the girl into allowing her to cut a sample of her hair (by claiming there was gum in her hair) and she gets a DNA test done which (allegedly) proves it’s her daughter.
Just a quick update from today’s Philly radio news - Yes, she collected some of the gir’s hair and yes, DNA tests were run on it, but those DNA tests didn’t come up with anything.
The problem was that the hair sample she collected didn’t contain anything from the follicle area, making the sample apparently worthless for DNA testing purposes. The authorities later colllected samples from the little girl’s mouth and both of the claimed mothers and were able to obtain conclusive DNA results from that.
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### Author:  [@Smeghead](https://boards.straightdope.com/u/Smeghead)
#### Post date: [March 4, 2004, 8:22pm UTC](https://boards.straightdope.com/t/dna-testing-for-the-common-citizen/232494/6 "2004-03-04T20:22:05Z")
> [@sevenwood](#):
>
> The problem was that the hair sample she collected didn’t contain anything from the follicle area, making the sample apparently worthless for DNA testing purposes. The authorities later colllected samples from the little girl’s mouth and both of the claimed mothers and were able to obtain conclusive DNA results from that.
Thanks for clearing that up. I was wondering about that.