Indeed. Several writers have referred to this sort of DNA as “fossil DNA”, as it provides a record of an organism’s evolutionary history. This would apply for both the non-functional and the functional duplicated genetic material.

I sometimes wonder whether or not all genes arose originally through duplication – ie is there a universal common ancestral gene, from which all surviving modern genes are descended from? Or is it more likely that there were a collection of such ancestral genes, each with its own lineage of descent all the way back to the first self-replicating molecules that stored information. Probably the original versions of all these genes would not have been DNA (they would have had the same information stored in a different molecular format, transmitting that information to descendent DNA at whatever point and by whatever process that resulted in the change to DNA for the genetic material).

I’m not sure if this question of ultimate gene ancestry is answerable by current techniques, or even answerable in theory. I suppose time will tell.

BTW I see a similarity between the two, because both are “not essential” DNA and they’re not constrained by the same selective pressure of a one-copy functional gene. This way they have the potential to mutate and create new genes or new regulatory functions.

A recent paper (which was commented by Ed himself ) suggests that the evolution of complex life forms was driven by energetic availability, which allows to maintain big genomes and to experiment with them.

My comment was just a thought about the opportunities raised by having more non-essential DNA.

Note that both posts came online within hours of each other, and we didn’t plan it. More convergence! Meta-convergence!

Since both gene copies remained functional, neither would have been considered to be “junk” DNA. It does share a mechanism of origin with some junk DNA, which arises from gene duplication events with subsequent function-destroying mutation of some of the copies.

But the loss of function mutation is most often irreversible. I think there are a few cases a sequence of previously non-functional DNA regained function or was co-opted for a new function, but these are very rare exceptions to the rule.

[EY: Fixed]