Prokaryotic Dna Is Reproduced With Blank Replication Forks

This is the second article in a series on the problems with Darwinian evolution. See https://jeffzimmer.com/2013/03/02/the-downsides-of-darwinian-evolution/ for context and the full recap of the evolutionary history of prokaryotic evolution.

Proposed explanations for the formation of new eukaryotes often invoke error-prone replication, as reviewed here. It has been much debated whether this so-called replication fork collapse might account for the origin of eukaryotes from prokaryotes. However, even if this process were proven to be the dominant form of DNA replication in the early eukaryotic common ancestor, the evidence isn’t strong.

Here we investigate an alternative mechanism: the proliferation of non-functional replisome like forks—similar to a potentially lethal cancer cell—that copy the genomic DNA without proceeding past the replication fork being copied. We present evidence that these replication forks produced by the late common ancestor of bacteria and archaea are what currently power prokaryotic genomes.

Why ‘Chloroplast Origins?’

The ancestral chloroplast genome was estimated to contain about 3.6 million base pairs (3.6 Mb), primarily comprising repeated sequences. It is presumed that the chloroplast gene pool contributed such widely varying amounts of DNA, perhaps even conserved among different eukaryotic lineages, and existed at about the same time that prokaryotic cells first appeared.

However, given that the metazoan ancestor of each animal kingdom possessed a small circular rRNA gene element called rDNA, all eukaryotes must have retained some unique genetic material. Moreover, the diverse spore forms of most major eukaryotic lineages have arisen from single-cell ancestors; and the protoarthrogenic archaea are thought to have gone through a three cell-division event when they escaped the early metazoan ancestor into an Earthless habitat. If there is a point in the lineage of the first protist, probably about 800-1,000 million years ago, then the ancestral eukaryotic rRNA gene also should have already existed, albeit with negligible sequence diversity.