Part I: Genetic Material
Lesson 1: Introduction to Cells, DNA, and Genes

The human body consists of trillions of cells. How do those cells know what function to carry out for your body?

Each cell has programs encoded in its DNA. The programs are sets of genes that become activated in different cell types (such as muscle cells versus nerve cells). These programs are permanently embedded in cells, but their activity can be turned up or down according to a person's age, lifestyle, and environment. The programmed information in genes is so critical that slight changes in genes can lead to inherited diseases, or make us more inclined to develop some diseases.