CHICAGO — A lobsterman from Maine, an oncologist from Nigeria and the first woman to lead a major American symphony are among the 25 people chosen for this year's MacArthur Foundation "genius grants," $500,000 that recipients can use however they wish.

Dr. Olufunmilayo Olopade, 48, left Nigeria for Chicago as a young woman and became an international leader in breast-cancer research, recently focusing on the molecular genetics of breast cancer in women of African heritage. Now director of the Center for Clinical Cancer Genetics at the University of Chicago Medical Center, she regularly returns to Nigeria to train doctors in the latest cancer treatments and research.

"To have an opportunity to leverage my position here to help underserved, underprivileged, understudied patients has really been my life's mission," Olopade said. "I'm blown away someone took notice."

The Chicago-based John D. and Catherine T. MacArthur Foundation also announced today a grant to lobsterman Ted Ames, 66, whose family has fished off the coast of Maine since before the Revolutionary War. Disturbed by the threat to the fishery ecosystem from over-harvesting, Ames conducts detailed scientific studies of spawning, habitat and fishing patterns — often starting with the anecdotal experiences of aging fishermen.

"What we're really trying to do is not play the role of Luddite, but take the good part of fishing and help it adapt to the 21st century," Ames said. "If the technologies we're using are too efficient or too destructive for the habitats to survive, we need to figure out a way to rein that in and modify our strategies and processes."

The other recipients:

Marin Alsop , 48, conductor. Named in July as music director of the Baltimore Symphony Orchestra, she will be the first woman to lead a major American symphony.

Terry Belanger , 64, professor and honorary curator of special collections at the University of Virginia in Charlottesville. The rare-book preservationist founded the Rare Book School, a nonprofit institute devoted to the histories of manuscripts, print and electronic text.

Edet Belzberg , 35, documentary filmmaker, New York. Belzberg is best known for "Children Underground," about a group of homeless children living in a Romanian train station.

Majora Carter , 38, urban strategist, New York. Carter is founder and executive director of Sustainable South Bronx, an organization that seeks to create new opportunities in the area for recreation, nutrition, transit and economic development.

Lu Chen , 33, assistant professor of neurobiology at the University of California, Berkeley. Chen's work with synapses sheds light on the biology of learning and memory.

Michael Cohen , 61, president of the Institute for Safe Medication Practices in Huntingdon Valley, Pa. Cohen is a pharmacist who has worked to reduce drug and drug-delivery mistakes.

Joseph Curtin , 52, who makes world-class violins at his studio in Ann Arbor, Mich.

Aaron Dworkin , 35, founder and president of the Detroit-based Sphinx Organization, which seeks to increase the numbers of minorities in classical-music careers by exposing children to music early and offering them access to training and instruments.

Teresita Fernandez , 37, sculptor, New York. Fernandez integrates architecture and common building materials into her work.

Claire Gmachl , 38, associate professor of electrical engineering at Princeton University. Gmachl works in the fields of optics and semiconductor laser technology.

Sue Goldie , 43, associate professor of health decision science at Harvard University School of Public Health. Goldie has identified new methods to improve women's health in underserved populations.

Steven Goodman , 48, field biologist at The Field Museum in Chicago. Goodman lives in Madagascar, where he works to document and protect endangered plants and animals.

Pehr Harbury , 40, associate professor of biochemistry at Stanford University whose work focuses on the structure and activity of proteins.

Nicole King , 35, assistant professor of molecular and cell biology at the University of California, Berkeley. King's work seeks to reconstruct the emergence of multicellular organisms that form the base of the animal kingdom.

Jon Kleinberg , 33, professor of computer science, Cornell University. His research topics have tackled a wide variety of practical problems.

Jonathan Lethem , 41, novelist, New York. His six novels include "Motherless Brooklyn" and "The Fortress of Solitude," which won the National Book Critics Circle award.

Michael Manga , 37, associate professor of earth and planetary science, University of California, Berkeley. Manga is a geophysicist who has explored phenomena ranging in scale from microscopic to planetary.

Todd Martinez , 37, professor of chemistry, University of Illinois, Urbana-Champaign. Martinez is a theoretical chemist who has developed new strategies that provide insight into the physical basis for chemical reactions.

Julie Mehretu , 34, painter, New York. Mehretu's work evokes multiple time periods and locales.

Kevin M. Murphy , 47, professor, University of Chicago Graduate School of Business. Murphy is an economist whose work has examined how economic forces influence social phenomena including unemployment.

Fazal Sheikh , 40, documentary photographer, Zurich, Switzerland. Sheikh uses portraiture to depict the faces of the world's displaced people, such as survivors of the Soviet occupation of Afghanistan.

Emily Thompson , 43, associate professor of history, University of California, San Diego. Thompson is an aural historian whose work has touched on everything from urban design to cinema studies.

Michael Walsh , 62, technical consultant, Arlington, Va. Walsh is a vehicle-emissions specialist who is working to improve the environment by reducing the impact of internal combustion engines.