The dN/dS ratio above one indicates the positive selection, around one show the neutral selection, whereas below one indicates the negative or purifying selection
. For Pakistani FAdV-11 strains, reported in this study, the dN/dS ratio was estimated to be 0.406, which indicates a negative or purifying selection
Thus, a lack of selective advantage for comparatively rare foreign-origin influenza A viruses, purifying selection
for endemic viruses, or both might be important mechanisms regulating the establishment of these viruses within the wild bird reservoir.
Among these, 54 unigenes were subjected to positive selection (Ka/Ks > 1), while the residues of 1064 unigenes were subjected to purifying selection
(Ka/Ks < 1).
According to M2 model, 64% sites were found under purifying selection
, 28% sites were under neutral evolution and only 6% sites were protected by positive selection.
The differences between observed value and fitted value could reflect the differences of purifying selection
. That means if S < 0, the variation of the gene suffers purifying selection
to become rare variation, and the mutation that occurs in these regions could be predicted more likely to cause certain kinds of diseases.
By mapping substitutions onto a gene tree of relationships among haplotypes, such models can characterize the relative contributions of purifying selection
or positive Darwinian selection as the ratio of those relative rates [omega] = [d.sub.N]/[d.sub.S].
The results strongly suggested that each of paralog pairs was subject to purifying selection
except for OsCLO7a/OsCLO7b.
Results suggest that PLAC1 is likely present in all placental species and has been under significant purifying selection
throughout the history of the clade.
Furthermore, analysis of duplicate genes in the tetraploid frog Xenopus laevis has shown that both copies were subject to purifying selection
, contrary to the prediction of the neutrality of one of the copies .
"Our method is a practical and successful way to screen for purifying selection
in non-coding regions of the genome using freely available data such as those from the ENCODE and 1000 Genomes Projects," says Dr Yali Xue, author from the Wellcome Trust Sanger Institute.
It has been recognized for a long time, first in principle by Fisher (1930), and then from comparative analysis of protein and, later, nucleotide sequences of homologous genes from different species, that a large proportion of mutations are thoroughly deleterious and are accordingly weeded out by purifying selection
. Thus, neutral mutations are the ones left over after the purifying selection
filter - these are the mutations that can exist as polymorphisms with the potential to fix and contribute to divergence among species.