Thus, bidirectional promoters are not maintained as highly conserved sequences in mammalian genomes, despite their close positioning between genes that are under negative (purifying) selection.
This ratio is currently employed to estimate if genes are under negative (purifying) selection (dN/dS < 1), positive (adaptative) selection (dN/dS > 1), or neutral evolution.
Although this effect was only marginally significant, it suggested that at least highly polymorphic CNVs are under negative (purifying) selection at miRNA genes.
If, on the other hand, we find that evolution in certain coding regions of non-autonomous copies are under negative, purifying selection, then this would be a strong evidence for them being functionally significant.
The ratio of the rate of nonsynonymous substitutions at nonsynonymous sites (dN) to synonymous (dS) substitutions at synonymous sites was estimated to figure out whether the coding region of a gene is under negative (purifying) selection (ω < 1), positive selection (ω > 1) or evolves neutrally (ω = 1).
Most singleton loci and paralogous genes were under negative, purifying selection when compared to their T. congolense homologs (i.e., ω << 1), which was reflected in a left-skewed frequency distribution of global ω and an average value of 0.219 (± SD 0.099).
In a long enough generation period, indels (or SNPs) with higher derived allele frequencies are more likely to be related to positive selections (adaptive selections), as those with lower derived allele frequencies tend to be under negative selections (purifying selections) for deleterious variants, in particular, the extremely rare variations.
Rather, with average dN/dS ratios <1, these protein regions all appear to be under negative or purifying selection.
Both the NTD and CTD appear to be under negative or purifying selection (dN/dS = 0.216 and dN/dS = 0.124, respectively).
The ratio of nonsynonymous (dN) to synonymous (dS) substitutions observed within the xenopus protein-coding sequences suggests that all genes are evolving under negative (purifying) selection.
