My Own Private Library Hamilton, Cayla M
The Georgia library quarterly,
04/2018, Letnik:
55, Številka:
2
Journal Article
Recenzirano
I like to consider myself an equal blend of my mother’s and father’s very disparate personalities, so it’s not surprising that my personal library is essentially a mash-up of the two systems we had ...going in my childhood home. Neither system ever sat well with me. In arranging my little library, I have opted for a set of middle-ground guidelines: 1. No dust jackets. 2. No dog-earing, highlighting, or annotating. 3. If I wouldn't give it at least three stars on Goodreads, I don't keep it. 4. There cannot be chaos. 5. No shelf can be pristine.
Convergent evolution has been demonstrated across all levels of biological organization, from parallel nucleotide substitutions to convergent evolution of complex phenotypes, but whether instances of ...convergence are the result of selection repeatedly finding the same optimal solution to a recurring problem or are the product of mutational biases remains unsettled. We generated 20 replicate lineages allowed to fix a single mutation from each of four bacteriophage genotypes under identical selective regimes to test for parallel changes within and across genotypes at the levels of mutational effect distributions and gene, protein, amino acid, and nucleotide changes. All four genotypes shared a distribution of beneficial mutational effects best approximated by a distribution with a finite upper bound. Parallel adaptation was high at the protein, gene, amino acid, and nucleotide levels, both within and among phage genotypes, with the most common first-step mutation in each background fixing on an average in 7 of 20 replicates and half of the substitutions in two of the four genotypes occurring at shared sites. Remarkably, the mutation of largest beneficial effect that fixed for each genotype was never the most common, as would be expected if parallelism were driven by selection. In fact, the mutation of smallest benefit for each genotype fixed in a total of 7 of 80 lineages, equally as often as the mutation of largest benefit, leading us to conclude that adaptation was largely mutation-driven, such that mutational biases led to frequent parallel fixation of mutations of suboptimal effect.
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