WASHINGTON (AP) _ The tiny energy source for cells in the body, called mitochondria, develop gene mutations over time in a process that may play a role in aging, researchers report.

In a study to be published Friday in the journal Science, a team of scientists say it has found that up to half of the mitochondria carried gene mutations in some people age 65, while such mutations were absent in the cells of younger people.

Mitochondria are small bodies in cells that provides the energy for the biochemical reactions that cells need to thrive. The mitochrondria have a set of genes that are independent of the genes contained in the chromosomes of a cell.

The study was prompted by speculation that a decline in the mitochondria is linked to the aging process.

The results show that the mitochondria genes do deteriorate with age, but it is not clear how this change affects cell life or mitochondria function, Dr. Giuseppe Attardi of the California Institute of Technology, senior author of the study, said in Science.