Anne Wojcicki, chief executive officer and co-founder of 23andMe Inc., speaks during the WSJDLive Global Technology Conference in Laguna Beach, California, U.S., on Wednesday, Oct. 26, 2016.

As if Amazon hadn't become a big enough part of our lives, the website is now increasingly the place people are going to find if they're of African heritage or if their children are at risk for certain rare genetic conditions.

DNA-testing companies that offer everything from ancestry information to tests for common inherited diseases are projecting record sales over the holiday season, with Amazon serving as a new marketplace for many of them.

Ancestry, 23andMe and dozens of other genetics companies all started selling on Amazon in the "home tests" category in the past year or two, with the bigger players working closely with Amazon to make that happen.

Among the first to initiate sales on the website was Ancestry, which started offering a DNA test for lineage and family connections through the marketplace in 2015. At that time, the company was selling 400 to 500 sets a day, a number that swelled to close to 1,300 a day by late 2016, said Vineet Mehra, Ancestry's chief marketing officer.

It's proved to be a larger-than-expected chunk of sales for Ancestry, which directs the bulk of its marketing and advertising to its own site.