orphan genes. Of the tens of thousands of enzymes of primary or specialized metabolism that have been characterized to date, none are orphans, or even of restricted lineage; apparently, catalysis requires hundreds of millions of years of evolution. Biological functions While the prevalence of orphan genes has been established, the evolutionary role of orphans, and its resulting importance, is still being debated. One theory is that many orphans have no evolutionary role; genomes contain non-functional open reading frames (ORFs) that create spurious polypeptide products not maintained by selection, meaning that they are unlikely to be conserved between species and would likely be detected as orphan genes. However, a variety of other studies have shown that at least some orphans are functionally important and may help explain the emergence of novel phenotypes. See Also De novo gene birth References Genomics Evolution