Evolutionary origin of orphan genes

Orphangenes are genes that occur in specific evolutionary lineages without similarity to genes outside of these lineages and have, therefore, alternatively been named taxonomically restricted genes. They were so far considered to emerge through duplication–divergence processes, but it isnowbecomingclear that they can also arise de novo out of noncoding deoxyribonucleic acid (DNA). This latter process may even occur much more frequently than previously assumed. It appears that genomes harbour many transcripts in a transition stage from nonfunctional to functional genes, also knownas protogenes, which are exposed to evolutionary testing and can become fixed when they turn out to be useful. Orphan genes may have played key roles in generating lineagespecific adaptations and could be a continuous source of evolutionary novelties. Their existence suggests that functional ribonucleic acids (RNAs) and proteins can relatively easily arise out of randomnucleotide sequences, although these processes still need to be experimentally explored