Gene Conversion - Evolutionary Importance of Gene Conversion

Evolutionary Importance of Gene Conversion

In the discussions of genetic diseases in humans, pseudogene mediated gene conversion that introduce pathogenic mutations into functional genes is a well known mechanism of mutation. In opposite, is there any chance for the pseudogenes to serve as templates from which during the course of evolution multiple changes in their single copy functional source genes which are potentially advantageous have been derived? The pseudogene-templated changes might eventually become fixed as long as they did not possess the deleterious effects. So, in fact, the pseudogenes can act as a source of sequence variants which can be transferred to the functional gene in novel combinations that are not tried so far and can be acted up on by selection. Lectin 11 (SIGLEC11) gene, which is a human immunoglobulin that binds to sialic acid can be considered as an example for such an gene conversion events which play a significant role in evolution. While comparing the homologous genes of human SIGLEC11 and its pseudogene in chimpanzee, bonobo, gorilla and orangutan, it came to know about the event of gene conversion of the sequence of 5’ upstream regions and the exons that encodes the sialic acid recognition domain which counts approximately 2kb by the closely flanking hSIGLECP16 pseudogene (Hayakawa et al., 2005). The three realizing points about this event have together suggested this as an adaptive change which is very evolutionarily important in genus Homo. Those includes that only in human lineage this gene conversion happened, the brain cortex has acquired an important expression of SIGLEC11 specifically in human lineage and the exhibition of a change in substrate binding in human lineage when compared to that of its counterpart in chimpanzees. Of course the frequency of the contribution of this pseudogene-mediated gene conversion mechanism to functional and adaptive changes in evolution of human is still unknown and so far it has been scarcely explored (Chen et al., 2007). In spite of that, the introduction of positively selective genetic changes by such mechanism can be put forward for consideration by the example of SIGLEC11. Sometimes due to interference of transposable elements in to some members of a gene family, it causes a variation among them and finally it may also cease the rate of gene conversion due to lack of sequence similarity which leads to divergent evolution.