Figure 1.

Possible transcriptional fates. For a complete gene duplication, a new copy is created that is most likely to maintain the isoform structure of the ancestor. Incomplete duplications result in only a portion of the ancestral gene being duplicated. This can lead to a truncated duplicate gene or a fusion transcript, where additional exons are acquired from flanking sequence. For 3′ truncations, transcription may persist until a polyadenylation signal or a new exon is encountered. For 5′ truncations, a promoter unlike that of the ancestral gene must be used if such duplicates are to be transcribed. Specific examples of known human-specific genes by type are indicated.