The decision invalidating the gene patents stunned many lawyers who follow such issues.

“It’s really quite a dramatic holding that would have the effect of invalidating many, many patents on which the biotechnology industry has invested considerable money,” said Rebecca S. Eisenberg, a law professor at the University of Michigan who has written widely on gene patents.

The Genomics Law Report, an Internet journal, called the decision “radical and astonishing in its sweep.” It headlined its article, “Pigs Fly.”

Although patents are not granted on things found in nature, the DNA being patented had long been considered a chemical that was isolated from, and different from, what was found in nature. But Judge Sweet ruled that the distinguishing feature of DNA is its information content, its conveyance of the genetic code. And in that regard, he wrote, the isolated DNA “is not markedly different from native DNA as it exists in nature.”

The immediate impact will be limited in part because the decision, made in a district court, does not apply to gene patents other than the ones it considered, and its value as precedent for other courts is limited.

Moreover, Myriad said Tuesday that it would appeal, and several lawyers said they expected the ruling to be overturned. Professor Eisenberg said “there isn’t a whole lot of doctrinal support” for considering DNA as information rather than as a chemical.

Even before an appeal is decided, the landscape could change in a way that would render the Myriad case moot. A ruling is expected soon from the Supreme Court in the so-called Bilski case. That case does not directly concern gene patents — it is about a fight over a method of hedging risk in commodities trading — but it gives the Supreme Court a chance to set new standards on what is patentable.

“We are still waiting, holding our breath for the Bilski case,” said Kari Stefansson, head of research at DeCode Genetics, which sells disease risk tests similar to those sold by Myriad.