genetic error
an error in the DNA code of a single gene. The genetic error may be due to a mutation that is spontaneous or one caused by an environmental factor, such as radiation. In either case, the error alters a gene’s ability to provide the proper instructions for cellular manufacture of an enzyme required to metabolize an important amino acid. A genetic error that becomes hereditary usually is not lethal to an embryo or fetus; the individual is able to survive birth and become a fertile adult, thus capable of transmitting the error to another generation of individuals. Some genetic errors, however, may result in fetal death or mortality for the individual before he or she reaches adulthood. More than 2,000 kinds of genetic errors have been cataloged.