In the face of local, tandem, segmental, and whole genome duplications, non-random gene loss may maintain some genes in low copy number [ 7, 65, 72].
There is thus no support for an ecological gradient hypothesis, in which the forms represent differentiated ecotypes which maintain some degree of gene flow.
The multiple, fragmented protein-coding regions and especially the presence of non-contiguous split tRNA genes [ 3] have been interpreted as evidence that N. equitans represents an ancient phylum-level lineage that maintained some ancestral gene structures and features of genome organization [ 4, 5].
We find evidence that either its populations in the remote Indian Ocean islands have maintained some limited gene flow with the remaining island populations until recently, or that they have colonized all three Mascarene islands very recently, such that N. ardentipes is best treated as synonymous with N. inaurata.
In Bm, the opposite occurred perhaps as a mechanism to maintain some of the essential genes in the smaller replicon.
A possible biological explanation for preferential attachment growth of metabolic networks is that novel enzymes created through gene duplication maintain some of the compounds involved in the original reaction, throughout its future evolution.
An extension of this hypothesis is that long introns may be maintained in some genes to reduce the number of mRNA products in the otherwise too-long time during which the genes are activated.
Namely, in agreement with the model, in the absence of any external ER agonists (control) all cells were capable of maintaining some basal level of gene expression, with the level of mRNA depending on ER in a non-monotonous way, noted for all four ER-dependent genes.
PEP-regulated genes often encode proteins involved in photosynthesis, whereas many NEP-regulated genes maintain gene expression functions.
