Title: Human disease - Diseases of genetic origin | Britannica
Headings: Diseases of
genetic
origin

Diseases of genetic origin
Factors relating to genetic injury
Heredity and environment
Chemical and physical injury

Content: Mutations that occur in the DNA of somatic (body) cells cannot be inherited, but they can cause congenital malformations and cancers (see below Abnormal growth of cells ); however, mutations that occur in germ cells—i.e., the gametes, ova and sperm—are transmitted to offspring and are responsible for inherited diseases. Each gamete contributes one set of chromosomes and therefore one copy (allele) of each gene to the resultant offspring. If a gene bearing a mutation is passed on, it may cause a genetic disorder. Genetic diseases caused by a mutation in one gene are inherited in either dominant or recessive fashion. In dominantly inherited conditions, only one mutant allele, which codes for a defective protein or does not produce a protein at all, is necessary for the disorder to occur. In recessively inherited disorders, two copies of a mutant gene are necessary for the disorder to manifest; if only one copy is inherited, the offspring is not affected, but the trait may continue to be passed on to future offspring. In addition to dominant or recessive transmission, genetic disorders may be inherited in an autosomal or X-linked manner.