# A digital DNA system favours the superiority of unidirectional inheritance over ‘Lamarckian’ inheritance

## TL;DR

A digital DNA system was created to compare unidirectional and bidirectional inheritance, showing that unidirectional systems have fewer mutations and are more stable.

## Contribution

The paper introduces a novel artificial system using DNA to store music, demonstrating evolutionary properties of bidirectional inheritance.

## Key findings

- Bidirectional systems have higher mutation rates and lack codon preservation mechanisms.
- Non-synonymous mutations occur at twice the frequency in bidirectional systems.
- Unidirectional inheritance is more stable and less error-prone than Lamarckian inheritance.

## Abstract

In biology, changes to a DNA sequence can impact protein sequence but changes to protein sequences (phenotype) do not flow back into DNA (genotype). A system with bidirectional information flow (i.e., both translation and ‘reverse translation’) remains a theoretical possibility for an independent origin of life or an artificial biosystem, but the recent development of digital data storage in DNA does just this: changes made to a digital file can be written back into DNA, meaning changes to ‘phenotype’ can be written back to ‘genotype’. To explore the evolutionary properties of such a system, we created an artificial system where synthetic DNA serves as genotype and music as phenotype. Audio can be output from a DNA sequence, then recorded and written to DNA as ‘codons’, enabling bidirectional information flow (DNA→music and music→DNA). Our results show that the mutation rate in a bidirectional system is much higher than for unidirectional information flow, and that, under reverse translation there is no mechanism for preservation of codon choice across generations. This has the effect of eliminating the impact of spontaneous synonymous mutations, a key benefit of a redundant genetic code. As a result, non-synonymous mutations are the only DNA-level changes that are transmitted across generations, and, as non-synonymous mutations can emerge at both ‘genotypic’ and ‘phenotypic’ levels, these occur at a two-fold higher frequency than in a unidirectional system. Our system holds some practical insight. First, for DNA read/write systems, it may be wise to avoid designing systems with ‘de novo reverse translation’ because the opportunities for mutation are higher; tracking genotype information from the preceding generation to guide this process may reduce error. Second, our system helps clarify how a ‘Lamarckian’ biological system might operate. We conclude that, were a ‘Lamarckian’ system of inheritance a feature of early genetic systems, it would likely have been short lived as the high frequency of mutation would risk driving the system to extinction. A system based on unidirectional information flow thus appears superior as there are fewer opportunities for mutational error.

In modern biology, the information for specifying protein sequences is stored in DNA. That information can be read from DNA, but the sequence of a protein cannot be converted back into a DNA sequence. This makes information transfer ‘unidirectional’ in biology and argues against the idea that changes to phenotype (protein sequence) can flow back into genotype (DNA). Two-way information transfer may have been a feature of very early RNA-based life, where genotype and phenotype were the same molecule type (RNA), and it is also a feature of prototype data storage systems that enable digital files to be written into and read from DNA. To examine how a ‘bidirectional’ system behaves, we created a system where, instead of protein sequences, music is stored in DNA. We allowed the music to evolve during playback, then wrote the mutated music back into DNA. This bidirectional system shows elevated mutation relative to a unidirectional system, so may explain why modern systems do not use this ‘Lamarckian’ process (so named in honour of Jean-Baptise Lamarck (1744–1829), who popularised the idea that information from the environment might directly lead to change in a species).