Adopted by white parents when she was just 3 months old, Abby Hasberry always yearned to find out who her birth parents were and whether she had any biological siblings. When she was 22, she asked adoption officials to contact her biological mother, but was disappointed.

Her biological mother "wasn't ready to meet me or talk to me because she hadn't told anyone she had me," Hasberry recalled.

For the next 24 years, Hasberry continued her search. Last year, she bought a DNA kit from 23andMe, sent in her sample, and checked off the box saying she wanted to know whether anyone else's DNA in the company's database matched hers.

She learned she had a cousin living in Philadelphia, who also was adopted, but knew her birth father's last name. The two women got in touch, and figured out from the few clues they had that their fathers were brothers.

Through some online detective work, Hasberry found seven probable siblings. She sent two of them DNA test kits that proved they were closely related.

"My cousin and I went to a big family reunion and met six of my seven siblings," said Hasberry, now 47 and living in San Antonio, Texas. "The reaction was amazing."

The same DNA tests that tell you (with varying accuracy) whether your ancestors were Greek or Norwegian, and whether you have a high risk of breast cancer or heart disease, also has the capacity to turn your family upside down.

Depending on how much you're willing to find out, you might land on a family tree with people you didn't even know existed.

Here's how it works:  For less than $100, you order a home test kit from one of several genealogy companies, and collect your own DNA by rubbing a swab inside your cheek or spitting into a tube. You send back your sample and your results are compared with those of everyone else in that database. Depending on how much DNA you share with any given person in the database – more than seven million samples in Ancestry.com alone — they estimate a possible relationship.

The 23andMe DNA Relatives tool estimates possible genealogical relationships by comparing your autosomal DNA (chromosomes 1-22) and X chromosome(s) with that of other members who are also using the DNA Relatives feature.

By logging into your private account, you can see all your matches, and if you and those matches agree, you can contact one another. Or you can opt out.

"Anyone who uses our DNA service can decide whether to share identifying information with other members or even decide if they want their information deleted," said Eric Heath, chief privacy officer at Ancestry.com.

Yet even if details aren't shared, it's possible to find out simply that there is a match out there somewhere. As Ancestry warns on its website: "You may discover unanticipated facts about yourself or your family when using our services. While we strive to give you control as you use the services, once discoveries are made, we can't undo it."

Sources such as social media and online searches can help locate biological relatives who may not want to be found. For example, obituaries are often a source of finding family members of the deceased who might then be contacted through Facebook.

This fact could prove startling to people such as Hasberry's birth mother, and also to sperm or egg donors who never thought they'd meet the outcome of their donation.

"The notion that an interested child would not be able to find you may be completely obsolete," said William Schlaff, professor and chairman of the department of obstetrics and gynecology at Thomas Jefferson University. "And egg freezing is open to the same kind of analysis. For people who know about social media and these kinds of detective adventures online, it's not very hard to figure this out or narrow it down. And it's going to get easier over time."

Schlaff pointed out that people share details about themselves much more easily than they did even a generation ago.

"Folks are very willing to share on Facebook and social media outlets things that I would never tell people," he added. "There are now sites and organizations that will help run these things down."

Every day, the Donor Sibling Registry, based in Boulder, Co., matches several people who are searching for biological relatives. "It's an innate human desire to want to know where we come from," said Wendy Kramer, DSR director. "It's about your identity, ancestry and medical background."

People born in the 1980s and forward – that's when sperm banks were created – usually know the sperm bank their mother used and have a donor number. For example, you can go to the DSR and do a search for all the California Cryobank donors to see whether there were any kids already posted for donor X. You can add your own posting and make yourself available for contact.

"If there were already people posted for that donor number, bingo, you're a match," said Kramer. "They get notified you're a match, you're in touch, you can send photos, medical information and messages."

Kramer and her then-10-year-old son, Ryan, started the group back in 2000 while searching for Ryan's biological father.

"My ex-husband had some infertility issues so we went the route of using an anonymous sperm donor and that was back in 1989 when there was only anonymity," recalled his mother. Born in 1990, Ryan was raised by his mother after his parents split up the next year.

In 2004, at 14, Ryan found his biological father – who was happy to be found.

"It was terrifying for me because my son was so vulnerable and his heart was so wide open," Wendy Kramer recalled. "His father had signed up for anonymity, which we respected."

But after Ryan contacted him, he "got two grandparents out of the deal and an amazing friendship with his biological father. We are all family," she said.

Others have a far different experience.

Though Hasberry found her biological siblings, and is enjoying getting to know them, her birth mother still refuses see her. Even the intervention of a brother who was raised by their mother didn't help.

"My brother told my mom that I found him but she tried to deny it at first," said Hasberry. "Then he told her he took the DNA test and she couldn't deny it. Then she basically shut down and said she didn't want to talk about it."

Resources

Sperm and egg donor registries:

Adoption registries:

DNA testing companies: