**7. Conclusions**

Given the copy-choice genomic repair mechanism present in today's ssRNA viruses, it appears that copy choice as a repair process may have emerged as early as 3.5 to 2.5 billion years ago when RNA was apparently the only genetic material. It is possible that the capability for strand-switching was a property of the earliest ribozyme polymerases.

In early protocells, the ssRNA genomes may have been segmented, as some ssRNA viruses are in the present day. Two protocells with damaged segmented genomes could have been able to generate undamaged progeny after fusion and then reassortment of segments. Present day ssRNA segmented genome viruses can repair damage in their genomes through both copy choice and segment reassortment.

The early stages of the evolution of genome repair proposed here are based on known capabilities of extant RNA viruses. Currently it is not known if these RNA viruses are the actual evolutionary descendants of early RNA life forms, or if they arose later. It has only been assumed here that the problem of dealing with damage to an RNA genome arises in the two cases, and that the solutions to this problem would be similar.

The earliest ssRNAs that formed folded structures that acted as ribozymes can be designated plus (+) strands. Such a ribozyme strand could have had polymerase activity and acted as an RdRp. The progeny ssRNAs that it synthesizes would be complementary to the corresponding parental (+) strands, and can be designated minus (−) strands. During the synthesis of (−) strands template-switching may have occurred.

#### *DNA - Damages and Repair Mechanisms*

When the ssRNA genome evolved to a dsDNA form, elements of the earlier copychoice recombinational repair processes appear to have been retained. In addition, the informational redundancy inherent in double-stranded DNA allowed the emergence of novel excision repair pathways (MMR, BER and NER) that could use the information in one strand to repair damage in the other strand. Other mechanisms (e.g. NHEJ and MMEJ) also emerged to deal with double-strand damages when an homolgous genome was not available. As eukaryotes evolved from unicellularity to multicellularity, and within an organism the germline became segregated from the somatic cell line, copy-choice recombinational repair was retained in the germline as a central feature of meiosis. Recombinational repair was also retained during mitosis, and as a general process for overcoming damage roadblocks to DNA replication*.*
