Exon Recombination

Eukaryotic genes consist of alternating blocks of protein-coding sequences called exons and noncoding sequences called introns.

Exon recombination is a process where the exons from the same or different genes recombine to produce novel combinations of exon-intron sequences, which might evolve into new genes.

The exon recombination can be mediated by non-homologous recombination or retro-transposition.

During non-homologous or illegitimate recombination, DNA strands with no sequence similarity can recombine and produce a novel gene structure.

Chronic granulomatous disease - a genetic disorder of the immune system is a good example. Many patients with this disease have a rare mutation in the phox gene coding for the enzyme NADPH oxidase.

The wild type NADPH oxidase produces reactive oxygen species such as superoxide upon infection and aids in phagocyte-mediated killing of the infectious agents.

In rare cases, the non-homologous sequences between exons 8 and 11 of the phox gene recombine, causing duplication of exons 9 and 10. This leads to the reduced activity of the enzyme NADPH oxidase. The impaired enzyme fails to generate enough reactive oxygen species to clear the bacterial infe