The genome sequence of each person is unique, with the exception of identical twins.  Although the frequency of base pair substitutions between different individuals is only 0.1%, obvious differences in physical traits are seen from person to person.  A trait is an observable characteristic of a person, such as height or temperament.  Genes encode proteins that direct the cells in our body to develop certain traits.  The environment we live in also influences the development of traits.  For example, your DNA may encode proteins that allow you to grow tall, but poor nutrition, certain infections, and traumatic accidents may prevent you from ever becoming tall.