ROCHESTER, Minn. (AP) - Mayo Clinic researchers are planning to create a human DNA bank using samples from 20,000 area residents, and they say it could become the largest population-based "biobank" in the United States.

The goal is to help researchers find ways to personalize the way illnesses are treated and prevented, based on patients' genetic characteristics.

Only Mayo Clinic patients who volunteer and give express, informed permission will be included.

"For it to be successful, we have to be able to have the cooperation of people willing to give DNA samples, coordinated with medical records," said Barbara Koenig, co-director of the Program in Professionalism and Bioethics at Mayo.

The biobank will not take volunteers until next year, and the Mayo Institutional Review Board must give final approval to the project.

Donating to the biobank won't be a one-time thing. An ongoing relationship will develop between the local participants and the biobank. For example, researchers might need to learn if a participant lives near a power pole.

The biobank also will ask participants for permission to make their samples and questionnaires "linkable" to their medical records.

"This is vital to study the effectiveness of treatments or prevention strategies over time. There is no other way to do this," Koenig said.

In addition to the population-based biobank, Mayo is planning three disease-specific biobanks focusing on mitochondrial DNA disorders, rare heart conditions and bipolar disorder.

"This is another form of philanthropy, in my mind," Mayo spokesman Bob Nellis said.