Figure 6.

Model of gene duplication under the preservation by entrainment (PBE) model. A. B2BA (Born to be Alike), shows duplicated genes with unaltered expression patterns that are preserved because of beneficial increase in dosage (20) in association with the condition-dependent expression of an interacting gene. B. B2BU (Born to be Useless) genes with initially divergent expression patterns, and with inappropriate condition-dependent responses, or interacting genes are most likely lost. C. B2BD (Born to be Different) when the derived expression pattern of a paralog at the time of duplication is shared with a different interacting gene (white negative sign), and when the effect of their combined products is beneficial under a distinct environmental condition the likelihood for preservation is increased. Color-coding represents condition-dependent expression patterns across multiple environments; empty boxes indicate no interacting gene with appropriate expression pattern. Lines represent the process of functional entrainment.