The purpose of DNA is to tell a cell how to function. Cells are the basic building blocks of human life. DNA, or deoxyribonucleic acid, is transferred from generation to generation of an organism, causing the cells in each succeeding generation to behave in similar ways. For example, brown eyes are caused by DNA coding which encourages certain chemical combinations in the human eye, combinations which result in brown coloring. This coding is passed from generation to generation, which is why a parent with brown eyes is most likely to have a child with brown eyes.