A New Function Evolved from Gene Fusion

What constitutes genetic difference among organisms? How do new gene functions originate in nature? Since the early days of molecular biology, we have known that homologous genes between species differ in DNA and protein sequence. Noncoding regions have also been evolving with repetitive sequences, transposable elements, and other elements continuously reshaping genomes of organisms. As more genomes of humans and other organisms are examined, it also becomes clear that species differ not only in these two genomic parameters but also in the number and kinds of genes.

Genes are subject to a life and death process: New genes have originated continuously throughout evolution. For example,Drosophila melanogaster contains 87 cuticle protein genes, while Caenorhabditis elegans contains no such genes in its genome (Rubin et al. 2000). If this is thought to be comparing too-divergent organisms, take a look at recently divergent sibling species. Drosophila teisseiri and Drosophila yakuba contain a gene called jingwei (Long and Langley 1993; Wang et al. 2000), which originated only 2.5 million years ago.D. melanogaster itself has a unique gene Sdic, which expresses particularly in the sperm tail and does not exist in even its closest relative species (Nurminsky et al. 1998).

New genes often give rise to new biological functions driven by adaptive Darwinian selection (Long and Langley 1993; Chen et al. 1997;Begun 1997; Nurminsky et al. 1998). New genes may even have controlled the origination of new species, for example, Odysseus, a homeobox duplicate gene in Drosophila (Ting et al. 1998). Such new genes are associated with two conspicuous changes consistent with origin of new functions: High protein substitution rates and drastic changes in gene structure.Drosophila is not the only organism whose genome has been found to originate new protein-coding genes differentiating one species from another. …