IT was a funny thing to be doing in a cocktail dress.

Debra Netschert, a financial analyst, was sitting next to her husband, K. C. Dustin, an equities salesman, and spitting into a test tube at a party last week in Chelsea to promote a DNA testing company.

As a soundtrack that included “Whole Lotta Love” blasted, the couple were submitting samples for tests that could reveal disturbing news, like his propensity to develop throat cancer or the chances of her having pregnancy complications.

But Ms. Netschert adopted the party mood, focusing, at first, on the less consequential details about her heredity. “I want to figure out why I have freckles,” she said.

It was taking a few minutes to fill the tube with the required amount of saliva, so Ms. Netschert had a dry-mouthed moment to consider what the couple might do if her husband turned out to be carrying a gene that could doom his offspring.