Genentech chairman Arthur D. Levinson is resigning from Google's Board of Directors, the Mountain View company announced earlier this morning. His departure comes shortly after Google Chairman and CEO Eric Schmidt resigned from the board of Apple, where Levinson is also a director. No reason for the departure was given in the statement, but it's safe to assume that it has something to do with the growing tension between Google and Apple, which is still being investigated by the FTC.