While, in some cases, the ability to integrate and excise foreign DNA may be selectively advantageous, the gain, loss, or rearrangment of gene cassettes could also be deleterious, selecting against functional integrases.
For s d ≥ 0.01, deleterious selection against housekeeper mutations had negligible impact on the likelihood of evolving a cancer with a mutator phenotype or on the waiting time to cancer (Fig. S1).
Interestingly, for a given number of housekeeper genes, increasing the strength of deleterious selection against housekeeper mutations led to a slight decrease in the waiting time to cancer (Fig. 6B).
In this way selection can act either directly against deleterious insertions or indirectly against deleterious chromosomal rearrangements produced by ectopic recombination between TEs [ 4, 5, 36, 70].
Positive selection (i.e., selection favoring changes in the protein sequence), neutral evolution and purifying selection (selection against deleterious alleles and thus, against changes in the protein sequence), is indicated by ω>1, ω = 1 and ω<1, respectively [ 35].
In fact, we observed that carcinogenesis could be actually accelerated by increasing the strength of selection against deleterious mutations, as strong selection against deleterious mutations served to increase the relative fitness of clones without deleterious mutations.
Purifying selection acts against TEs mainly in three ways: (1) against deleterious effects of TE insertions on neighboring genes [3], [4], (2) against deleterious effects of TE-generated expression products [5], and (3) against deleterious products of ectopic recombination among dispersed homologous TEs [6].
This observation suggested that mtDNA was under purifying selection against deleterious nonsynonymous mutations, coinciding with previous study23,24,25.
Wang, Y. et al. Pathway to neural resilience: Self-esteem buffers against deleterious effects of poverty on the hippocampus.
