Are small insertions always single-stranded?

Question

[LayneSadler]

Are small insertions (indels) always single stranded?

In the example below a break in the lower strand is repaired with the insertion of G. It could have inserted more than 1 nucleotide though.

Is it true that small insertions would never insert on both strands... as seen in large-scale SV insertions or CNVs?

Answer 1

[WouterDeCoster]

I don't know if there is a difference between small and large indels, but for sure this single-stranded event will very soon afterward either get repaired by the cell (DNA mismatch repair, etc) or the other strand will get the same variant (although anticomplementary) due to DNA replication in the cell cycle.

So it should not stay single stranded as you show in the picture.

[LayneSadler]

Wow. So a matching nucleotide will likely be inserted on the other side? Thanks!

[Jean-Karim Heriche]

Or the extra nucleotide gets removed. I don't know which is more likely and it certainly depends on the type of cell (e.g. bacteria, cancer cells...).

[WouterDeCoster]

This probably hasn't been tested (?) but I'd expect a healthy cell to fix most of its DNA damage, or die trying. Indeed things will be different in cancer or heavily stressed cells...