Genetic mutations are changes in a DNA sequence that can occur at any time in an individual’s lifetime and in different cell types. They can lead to diseases such as autism, cystic fibrosis, or cancer. This interactive illustrates how two cell lineages (germline and somatic) are generated during development and that mutations can occur in either lineage. Only some mutations cause disease, depending on where in the genome they occur and in which cell type. Mutations that occur earlier in development are more likely to affect a greater portion of the body than those that occur later in life.