Somatic recombination

Somatic recombination, as opposed to the genetic recombination that occurs in meiosis, is an alteration of the DNA of a somatic cell that is inherited by its daughter cells. The term is usually reserved for large-scale alterations of DNA such as chromosomal translocations and deletions and not applied to point mutations. Somatic recombination occurs physiologically in the assembly of the B cell receptor and T-cell receptor genes (V(D)J recombination),^[1] as well as in the class switching of immunoglobulins.^[2] Somatic recombination is also important in the process of carcinogenesis.^[3]

In neurons of the human brain, somatic recombination occurs in the gene that encodes the amyloid precursor protein APP.^[4] Neurons from individuals with sporadic Alzheimer's disease show greater APP gene diversity due to somatic recombination than neurons from healthy individuals.^[4]

Plants

See also: Bud sport

Intrachromosomal homologous recombination in Arabidopsis thaliana plants was found to occur in all organs examined from the seed stage to the flowering stage of somatic plant development.^[5] Recombination frequencies were typically in the range of 10⁻⁶ to 10⁻⁷ events per genome.^[5] A. thaliana mutants selected for hypersensitivity to X-irradiation also proved to be simultaneously hypersensitive to the DNA damaging agents mitomycin C and/or methyl methanesulfonate.^[6] The mutants were also deficient in somatic homologous recombination.^[6] These findings suggest that repair of some types of DNA damage requires a recombinational process that was defective in the mutants studied. In nature, plants are continuously exposed to UV-B (280–320 nm) radiation, a component of sunlight that damages the DNA of somatic cells.^[7] Cyclobutane pyrimidine dimers (CPD) are a type of damage induced by UV-B. In A. thaliana, homologous recombination appears to be directly involved in repairing CPD damage.^[7]