How is it that all cells in our body have the same genes, yet cells in different tissues express different genes? A basic notion in biology that most high school students fail to conceptualize is the fact that all cells in the animal or human body contain the same DNA, yet different cells in different tissues express, on the one hand, a set of common genes, and on the other, express another set of genes that vary depending on the type of tissue and the stage of development. [29:12]