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.
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]