The deleterious effect of FL elements does not appear to completely prevent fixation of L1 elements, yet there are very few ancient elements in the Anolis genome.
This widespread fixation of L1 elements suggests that, as in stickleback, the turnover model cannot explain the scarcity and young age of L1 elements found in Anolis.
Elucidation of the evolutionary constraints that have shaped fixation of transposed elements within human and mouse protein coding genes and subsequent exonization is important for understanding of how the exonization process has affected transcriptome and proteome complexities.
It remains true, however, that purifying selection is insufficient to prevent the fixation of truncated elements, which constitute the majority of the inserts.
We also figured out partial sequence of the entire loci is highly conserved in mammalians before the birth and provided evidences and correlated factors for the early fixation of conserved elements.
This suggests not only that the Anolis genome is similar to fish in its autonomous nLTR-RT repertoire, but also that a similar mechanism is preventing the fixation of FL elements in nonmammalian genomes.
On the other hand, the observed upper limit to the chromosome-level exon Alu density may indicate that the fixation of Alu elements in the coding regions of genes is further determined by the biological tolerance.
For weakly deleterious sites, fixation of the element insertion by drift may occur, thus preventing selective loss, and, in this way, the selective removal of weakly harmful elements will typically be attenuated in small populations.
simulans Anderson et al. [15] showed patterns of evolution at the mtrm gene that are compatible with both adaptive protein evolution and the sequential fixation of meiotic drive elements.
Freeze drying of the samples prevented leakage of elements during fixation, allowing us to detect tissue-specific distribution of elements with low abundance such as Cd (Fig. 4b).
