Determinants of the genetic code’s exceptional permissiveness for overlapping genes

Identify the precise features of the standard genetic code that confer exceptional flexibility for supporting long overlapping genes, beyond codon degeneracy and the pattern of synonymous mutations.

Background

By comparing overlaps under shuffled genetic codes that preserve either codon degeneracy (type I) or synonymous structure (type II), the authors find that the standard genetic code is uniquely permissive for overlapping genes, outperforming both classes of randomized codes.

These results imply that neither degeneracy alone nor synonymous structure alone explains the observed permissiveness, leaving the precise contributing features of the natural code unresolved.

References

Our study leaves unanswered the question of what precise aspect of the standard genetic code makes it so flexible -- as neither codon degeneracy nor their synonymous structure were sufficient on their own.

— The fitness landscape of overlapping genes  (2604.00602 - Kirsch et al., 1 Apr 2026) in Discussion