- [Narrator] You might've seen one of these before,
an at-home DNA test.
The boxes might look small,
but they're making a big impact on some people's lives.
Kits like these have exploded in popularity
over the past five years.
Most people take them
because they wanna know more about their background,
like what countries their ancestors were from
or if they're really related to George Washington.
And for many, the results are what they expect.
But for others,
the results can radically change their lives.
- A lotta people take these tests
hoping for something entertaining.
Maybe they heard they're Italian or German
and they think it would be fun to find out more.
But often when they get the results back,
they're surprised by what they find.
- [Narrator] So how can that happen?
Meet Sally.
We made her up to show how this can work.
Sally took DNA tests with her family,
her mom, her dad, her brother, and her sister.
Six weeks later, they went online to check their results.
The company provided a long list of genetic matches
ranked in order by the amount of DNA shared
and measured in a unit called centimorgans.
- Often DNA testing companies
will return a list of your genetic matches to you.
They usually rank your genetic matches
from the highest number of centimorgans
you share with someone
to down to the fewest number of centimorgans.
So you're gonna expect to share the most centimorgans
with the people who are closest to you.
- [Narrator] Parents and children
share around half of their DNA.
Siblings share a little bit less.
Half-siblings share around a quarter, you get the idea.
So naturally, Sally saw both of her parents
at the top of the list.
They each shared around 3400 centimorgan in common with her.
Next she saw her brother, who shared 2700 centimorgan.
And then her sister, who she shared around 1700 centimorgan.
This was the first red flag for Sally.
Why do these numbers look so different?
It turns out 1700 centimorgan
isn't enough for Sally's sister to be her full sister.
But it is enough for them to be half-siblings.
They talked to their mother
and it turns out she had an affair.
- In our hypothetical example,
Sally found out that her mother had an affair,
but that's not the only thing that people find out.
Many people have been able to identify
their biological relatives when they were adopted.
Other people have discovered
that they were conceived using sperm donations.
- [Narrator] But that wasn't the only surprise in store
for Sally and her family.
Sally's father Andy checked out his DNA results too.
He already knew about the affair,
so he wasn't surprised
that one of his daughters wasn't a match.
But he did notice several names high up on the list
that he didn't recognize.
When Andy was a college student,
he made sperm donations in order to earn extra money
and he assumed that his sperm donations
would always remain anonymous.
But now many people who were donor-conceived
can find their sperm donors via DNA testing.
This person shared 3400 centimorgan with Andy,
and as it turned out. was his biological son.
So Sally's been through a lot.
She's learned that her sister is her half-sister
and now she has another half-sibling on her dad's side.
Sally was reeling from the twist
and turns in their family DNA when
the phone rings at Sally's home.
(phone rings)
It's the police.
They found Sally's DNA in a database.
- Many people take more than one test.
They want to expand the number of relatives
they can potentially match with.
Another way to do this is to take the results
and put them on a website that has a public database.
Many consumers, if not most,
are taking these tests for purposes of genealogy.
They're not expecting that law enforcement
might be interested in using the results
to track down possible criminals.
- [Narrator] But increasingly,
law enforcement officials use the databases as well,
working with genealogists to try and solve crimes,
mainly cold cases and missing persons.
Here's how that works.
Police take DNA from a crime scene,
it usually comes from the victim or a suspected criminal.
Then police upload the DNA into one of the big DNA databases
and look for genetic matches between the crime scene DNA
and others who have tested.
- When there is a genetic match, genealogists are able
to use the information in the databases
to build a rough family tree.
They're then able to use publicly available information,
such as obituaries or wedding announcements,
which are often available online, to get more names.
They might look at Facebook and other social media postings,
again, to find more connections between people.
Once investigators and genealogists
have created a family tree,
the investigators can narrow down the leads
and figure out from the family tree
who was born at the most likely time
that the suspect was born,
who was living in the most likely place
where the crime was committed, or someone disappeared.
- [Narrator] For Sally's family,
the call from the police helped solve a mystery.
Law enforcement used clues from their family tree
to find a missing person.
To be clear, Sally's experience with DNA
is not the typical one.
It's not every day that someone discovers a family affair,
a distant half-brother, and helps solve a crime.
But all of these things do happen
and they're happening more often
as DNA tests gain popularity.
- The growing popularity of DNA testing,
and the increasing sizes of the databases,
have really raised privacy concerns.
Decades ago, people were promised anonymity
when they gave up their children for adoption
or when they participated in sperm donation,
and now suddenly, thanks to DNA testing,
people are able to track down
the identities of these people.
There are a number of people
who say that they don't wanna do DNA testing
because they wanna preserve their genetic privacy,
but the fact is that even if you choose not to do a DNA test
a distant cousin that you don't know and may have never met
is possibly making another decision
and that decision is gonna affect your privacy as well.
Some of your DNA may be used by people
to unravel family secrets or track down potential criminals
or all the other uses that it's currently being used for.
Even some uses that we haven't anticipated yet.