You would be consigning yourself and all future generations on the ship to slavery in a eugenics cult from which there is no escape. There are a small number of people available to fill limited roles, so you must hold that role for your entire life until there are enough trained replacements to do it. The replacements would also not have a choice and would begin being trained for that role from an early age. Since the ship has a maximum capacity for people all breeding would need to be centralized and required of women. It's a problem if people live too long as they are taking food from the younger, healthier generations; so you might even see ritual suicide in elders being required.