However, if both ribotypes were present within the genome of the most recent common ancestor of Symbiodinium C100 and C109, processes of concerted evolution may not have had sufficient time to homogenize the rDNA arrays of both taxa.
Previous studies of the 5S rDNA gene family carried out in four species from the Western Atlantic showed two types of this gene in two species but only one in the other two, under processes of concerted evolution and birth-and-death evolution with purifying selection.
The process of concerted evolution homogenizes rDNA arrays and theoretically removes variability among repeats within the genome.
First, the ITS is part of a genomic region known to be affected by the process of concerted evolution [ 47].
These copies are usually very similar due to the process of concerted evolution, operating by e.g. unequal crossing over and gene conversion (e.g. [ 17, 18]).
The very low divergence between repeat units, even at synonymous positions, suggests that the repeats are kept nearly identical through a process of concerted evolution.
The very low divergence between repeat units, even at synonymous positions, strongly suggests that the units are kept nearly identical through a process of concerted evolution analogous to the preservation of sequence homogeneity in rRNA clusters.
Thus, functional or even non-functional sequences could be kept and homogenized by gene conversion and unequal crossing over via the process of concerted evolution, leading to the current set of observed variant gene classes.
In contrast to the ITS, ndhF is a chloroplast gene and thus likely not susceptible to the process of concerted evolution, although nuclear capture of chloroplast DNA is possible [ 48] but untested in this case.
The lack of signal on one of the homoloques may be a direct consequence of sequence elimination due to unequal crossing-overs, often related to a process of concerted evolution in tandemly-repeated genes [ 114] or by the activities of repetitive DNA such as TEs [ 59, 115].
In allopolyploid species, it was shown that the process of concerted evolution also affects homeologs, resulting in a preferential retention of one of the parental repeat copies, as demonstrated in polyploid cottons (Wendel et al. 1995) or tobacco (Kovarik et al. 2008).
