Human chromosome 2 has always intrigued primate biologists; it formed from the fusion of two mid-sized ape chromosomes and is the only cytogenetic distinction separating humans from apes. At the molecular level, however, the differences among the species are much more complex.
Bork's team systematically searched the complete genomic sequences from a broad range of taxa (mouse, rat, roundworm, fruit fly, mosquito, and pufferfish) for single-copy genes that had evolved more than one copy in humans. "Gene duplication is known to play a leading role in evolution for the creation of new genes," explained Francesca Ciccarelli, Ph.D., lead author on the study. The key to this, however, is that the duplicated copies of genes very quickly evolve functions that are significantly different than those of their progenitors.
Natural selection acts on gene duplications, most often by deleting them from the gene pool or by degrading them into non-functional pseudogenes. This is because fully functional duplicated genes, in combination with the corresponding parent gene, produce abnormally abundant quantities of transcripts. This overexpression often alters the fragile molecular balance of gene products on a cellular level, ultimately resulting in deleterious phenotypic consequences. If these duplicated genes acquire new functions, however, they may confer a selective advantage to an organism, leading to the rise of lineage-specific genes over evolutionary time.