In most multicellular organisms, every cell carries the same DNA, but this genetic information is used in varying ways by different types of cells. In other words, what a cell does within an organism dictates which of its genes are expressed.
Most enlisted positions require four years of active duty. If you join the Navy through an officer program, you must serve at least four of your eight years on active duty. However, pilots and flight officers must serve a minimum of eight to 10 years of active duty. Dentists, Medical Service Corps officers and nurses must serve a minimum of three years of active duty.
Officers are the Navy's leaders. They guide enlisted Sailors and provide the know-how and expertise to get the job done. Active duty service terms typically last two to six years. Deployment can last between a few weeks to six months, but the length varies depending on the size of the ship and its mission.