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.
You must have served on active duty as a JAG officer and you must be over 21 years of age at the time of your appointment as a Reserve JAG officer. You must also be under 40 years of age as of the date you begin your reserve commitment so you can complete 20 years of service before your 60th birthday.