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Are there any alternative systems to RNA/DNA that can pass on genetic information? I'm not talking about stuff that essentially just uses the central principle and structure of DNA with some of the specifics changed, like XNAs which just use a different sugar backbone, or Hachimoji DNA which just adds on extra base pairs, I'm talking about plausible hypothesised systems that are radically different to what we use now.
One of the most fascinating and out-there proposals I've come across is Graham Cairns-Smith's clay hypothesis, which posits that clay crystals were the first genetic material. The idea here is that crystal growth is a form of self-replication that "reproduces" its arrangement, and can even transmit defects. The pattern is then "passed along" when the crystal breaks (scission) and continues to grow independently from the original crystal. Eventually, a "genetic takeover" of sorts happens, where clay crystals that trap certain forms of molecules to their surface improve their replication and catalyse the formation of increasingly complex proto-organic molecules that eventually take over the original genetic substrate as the new genetic material.
Schulman, Yurke and Winfree in their paper "Robust self-replication of combinatorial information via crystal growth and scission" use the same principles to create a set of DNA "tiles" that replicate its sequence of tiles through crystal growth. Each tile has "sticky ends" that hybridise with each other, and under appropriate growth conditions, complementary sticky ends hybridise, while non-complementary sticky ends are unlikely to interact. The interaction of these sticky ends allows for accurate sequence replication during growth, and once crystal growth has propagated the sequence, these additional layers are then "cleaved" off through mechanical scission.
However, that's the only truly interesting and novel idea surrounding this I am aware of, and I'm not entirely sure if and how this system of replication could achieve a significant level of biological complexity (save for a "genetic takeover" that effectively replaces the original system). I can't help but feel there are probably more such systems that could be posited.
You might be able to come up with some system of proteins that replicate and pass on genetic information. This was the original hypothesis before the genetic properties of DNA and RNA were discovered.
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