Accumulating mutations lead to frequent adaptation of non-genic loci and de novo gene birth

Over evolutionary timescales, genomic loci switch between functional and non-functional states through processes such as pseudogenization and de novo gene birth. Here we ask about the likelihood and rate of functionalization of non-functional loci. We simulate an evolutionary model to look at the contributions of mutations and structural variation using biologically reasonable distributions of mutational effects. We find that a wide range of mutational effects are conducive to functionalization, thus indicating the ubiquity of this process. Interestingly, in the special case of de novo gene birth, whereby non-functional loci begin to express a functional product, we find that expression level changes lead to rare, extreme jumps in fitness, whereas sustained adaptation is driven by product functionality. Our work supports the idea that the potential for adaptation is spread widely across the genome, and our results offer mechanistic insights into the process of de novo gene birth.