DNA codes for protein through the intermediary of RNA. For the longest time, it was believed that this flow was unidirectional. It is now clear that this is not entirely true. Nevertheless, this model frames the basics of our understanding of molecular biology, and while the study of genetics focuses on variation that originates in DNA, we must always be mindful that this variation has its action by eventually interfering with protein function. Refer to UpToDate topics on genetic variation for more information.
