Question

Explain the two main mechanisms of gene duplication (not polyploidy) described in class. How can you identify which mechanism produced a given gene? That is, describe all of the differences you would expect. What is the significance of gene duplication to evolution?

Answer 1

Gene duplication is the main mechanism that helps in creating the genetic novelty of organisms by generating new genes thus contributing to evolution. It is the process by which one gene gets duplicated and is present in the same genome as paralogs and in different genomes as orthologs. Studies on evolution by gene duplication have concluded that the new genes arise and the evolution of invertebrates to vertebrates might have happened only by whole-genome duplication. Hence, gene duplication has contributed to the evolution of developmental programs and new gene functions in several organisms. Example: The distinctive feature of the angiosperm genome is the extent of gene duplication that has led to angiosperm evolution. Gene duplication may be caused by two main mechanisms- unequal crossing over or retroposition (also called chromosomal duplication).

Unequal Crossing Over- This mechanism produces continuous repeats of DNA sequences. Duplicated regions might contain a part of a gene or entire gene depending on the position of crossing over. If introns are present in the original gene, then it will be present in the duplicated gene.

Retroposition- In this mechanism mRNA is reverse transcribed to cDNA and inserted into the genome. Retroposion can be characterized by the molecular features such as lack of introns and regulatory sequences, presence of poly-A sequence, and flanking short direct repeats. Because of the random insertion of cDNA into the genome, the duplicated gene is unlinked to the original gene.