One of the most important activities of a cell is the production of proteins that fulfill major roles in the cell--structural, enzymatic, hormonal, and more. The instructions for building all the proteins an organism needs to make are located in the DNA molecules of the chromosomes which never leave the nucleus of the cell. However, the actual synthesis is carried out by the ribosome’s, small structures which either float freely in the cytoplasm or are attached to membrane networks that snake their way through the cell--in either case, outside the nucleus. Gene mutations occur in two ways: they can be inherited from a parent or acquired during a person’s lifetime. Mutations that are passed from parent to child are called hereditary mutations or germ line mutations (because they are present in the egg and sperm cells, which are also called germ cells). This type of mutation is present throughout a person’s life in virtually every cell in the body. Mutations that occur only in an egg or sperm cell, or those that occur just after fertilization, are called new (de novo) mutations. De novo mutations may explain genetic disorders in which an affected child has a mutation in every cell, but has no family history of the disorder. Acquired (or somatic) mutations occur in the DNA of individual cells at some time during a person’s life. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation. Mutations may also occur in a single cell within an early embryo. As all the cells divide during growth and development, the individual will have some cells with the mutation and some cells without the genetic change. This situation is called mosaicism. Some