DNA is the source of information for making proteins in the ceil. The section of DNA is called gene. For example, the height of a plant depends on the hormone. The amount of hormone depends on the process of its formation. A protein is important for this process. If this protein works efficiently a lot of hormones will be made. If the gene responsible for that protein has an alteration, this will make the protein less efficient. The amount of hormone will be less and the plant will be short. Thus, traits get expressed.
