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

Different sets of genes are active during different times of a person's life. The human body develops from the time of fertilization to old age. The changes that occur in our bodies as we develop are often due to changes in gene activities that are regulated by our stage of development. This is known as developmental gene regulation. Different sets of genes are turned on and off as we develop and age. For the most part, the genes themselves remain constant.