Lesson 1 How Traits Change – We learned that changes (mutations) to genes can result in changes to proteins, which can affect the structures and functions of the organism and thereby change traits. Each chromosome consists of a single very long DNA molecule and each gene on the chromosome is a particular segment of that DNA. Instructions for forming species’ characteristics are carried in DNA. All cells in an organism have the same genetic content but the genes used or expressed by the cell may be regulated in different ways.