In theory, evolution provides a logical answer: unfit individuals are less likely than fitter folk to be able to maintain the symmetrical development of their bodies when exposed to stress and disease.
When considering perfectly symmetrical rates of evolution one copy is expected to evolve slower than the other due to the random variation of the d n/d s measurements.
Third, paralogs residing in close genomic proximity are likely to share their ancestral regulatory elements [ 24, 35] the ancestral gene neighborhood (local synteny) as well as short-range chromatin effects [ 30, 56], which are thought to cumulatively serve to increase the likelihood of symmetrical rates of paralog evolution under both selective [ 57- 59] or neutral regimes [ 60].
Moran et al. [ 41] showed recently that B. aphidicola sequence evolution is not symmetrical, and its sequences can only evolve towards shrinkage, since the observed insertions are not bigger than a few bp, and are mainly caused by polymerase slippage.
Identification methodology is presented and the model validated by comparing experimental and predicted evolution of hysteresis loops during symmetrical and non-symmetrical total strain LCF testing.
Multiple researchers turned their attention to measuring the degree of sequence divergence among paralogs in a diverse set of genomes to determine whether paralogs, on average, exhibit symmetrical or asymmetrical rates of molecular evolution.
However, in a truly symmetrical case the increase in the rate of evolution in the fast-evolving copy will be of the same magnitude as the decrease in the rate of evolution of the slow copy.
Informally, the plots in Figures 27 and 28 indicate that small families may preferentially grow (under higher degree models) or shrink (under low degree models) whereas the evolution of large families tends to a symmetrical random walk.
For example, the model of evolution applied to the morphological data assumed symmetrical rates of change from one state to another (Lewis, 2001), but a more complex model can implement asymmetrical rates from one state to another (Schultz & Churchill, 1999).
We fitted three standard models to the data and the phylogeny, known as the "equal", "symmetrical", and "all different" rate models and added a custom model assuming a three stage model of evolution.
