- [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.
