SAN FRANCISCO — For DNA testing companies, the genetic code that customers pay to have analyzed is a gift that keeps on giving. Not only do these companies profit from DNA analysis, but they stand to make money for decades more marketing people’s data to the highest bidders.

Ancestry, which controls a database of more than 5 million DNA samples, is one of the companies marketing its genetic storehouse. The Utah-based company has no formal policy on what partnerships it will or will not pursue, but company officials say they’d never risk a collaboration that could be viewed as exploitative. “We only want to do research totally on the up and up,” said Eric Heath, chief privacy officer for Ancestry.

But when customers sign up to have their data shared with research partners of Ancestry, 23andMe and other companies, they are taking a leap of faith. Ancestry’s main research partner is a Google subsidiary named Calico, which researches therapies aimed at extending the human life span. Unlike public institutions, California-based Calico discloses little about its DNA work, and many view it as a vanity project for Silicon Valley billionaires seeking breakthroughs to extend their own lives.

“Calico was founded around the idea of making people live forever,” said John Simpson, an advocate with Consumer Watchdog, a nonprofit group that monitors Google and other Silicon Valley players. “It is very murky, and they are not very forthcoming about what they are doing.”

Marcy Darnovsky, executive director for the Center for Genetics and Society, said that Ancestry’s millions of customers are likely unaware that, when they click the “consent to research” box, their DNA information is being used by a private company for private gain.

“If Google is behind it, it is important for people to understand what they are doing, and the money behind it,” said Darnovsky, whose Berkeley-based group monitors the tech industry and bioethics issues.

Supporters of commercial DNA testing say there is nothing wrong with this form of molecular monetization. The databases of DNA-testing companies hold the potential to explore the genetic origins of diseases. Private capital will be needed to fully analyze and explore this data, they argue.

But DNA is a person’s most unique identifier, and privacy experts say the sharing of this data increases the risk it could be stolen or exploited. Heath said Ancestry has protocols in place to protect people’s private information.