More frequent fixation of allelic variants by positive selection could be balanced by a lower rate of fixation of slightly deleterious alleles on the X chromosome.
Surgical experience is very important, but this factor has been balanced by patient selection criteria.
Nevertheless, variation that is balanced by maternal selection is likely to show elements of heterozygous advantage and be resistant to depletion by genetic drift.
If selection for functionality is balanced by counter-selection from the host immune system, this could trigger a periodic cycle in which strains with and without fha repeatedly out-compete each other.
This selection is balanced by interactions among different target substrates, ubiquitin ligases, ubiquitin ligase adapter proteins, and chaperons.
The dotted line in each graph in Figure 7 are for completely equal usage of all codons, when mutation bias to A/T is exactly balanced by selection to G/C; thus one interpretation is that genes to the left of the dotted lines are dominated by mutation while those to the right are dominated by selection.
Genes/amino acids with completely even codon usage would occur only when the mutation bias toward A/T is exactly balanced by selection toward G/C.
Alternatively, these two divergent haplotypes may be balanced polymorphisms maintained by frequency-dependent selection, spatially varying selection pressures, or overdominance.
The cumulative effects of potential selection forces are hard to assess by virtue of the difficulty in the quantitative analysis of selection forces, and the picture is further complicated by the fact that a particular CNV allele is not, of necessity, balanced by selection.
A second genetic process that may help to explain an enrichment of positive selection on polygenic disease genes is balancing selection mediated by antagonistic pleiotropy, or other processes including overdominance or frequency-dependent selection.
