Dani Shapiro’s 2019 memoir “Inheritance: A Memoir of Genealogy, Paternity and Love” (recently published in paperback by Anchor Books) was an exploration of DNA and the many secrets it can contain.

In 2016, Shapiro had submitted a kit for DNA analysis through Ancestry.com. She didn’t expect much.

“I spent 54 years believing that I absolutely understood my own identity,” she told The New York Times.

Instead, she received quite a bombshell. The test revealed she was only half Jewish, and unrelated to the woman she had thought of as her half-sister.

Shapiro had always known that she had been conceived at a fertility clinic in Philadelphia. But while this was true, it turned out that her biological father was a sperm donor — a non-Jewish doctor from Oregon who had gone to medical school at Penn.

In some ways, this explained a lot: She had always felt out of place in her birth family; strangers would often comment that she didn’t look Jewish. The discovery was more than just a matter of donor sperm; it rocked the foundation of her world.

The month after her book was published, Shapiro launched a podcast, “Family Secrets,” in collaboration with iHeartMedia. Since then, it has become an iTunes Top 10 podcast and has been downloaded more than 10 million times.

Season 3 kicked off in early February, with listeners calling in to share their own family secrets revealed by DNA tests. It’s a craze that shows little signs of dying down; a study estimated that by 2021, around 100 million people will have had their DNA mapped by companies like Ancestry.com and 23andMe.