Genome Stability and Evolution: Attempting a Holistic View

The reason why the DNA content, chromosome number and shape, and gene content of eukaryotic genomes vary independently remains a matter of speculation. The same is true for the questions of whether there is a general tendency for increase or decrease of genome size and chromosome number and whether genome size and/or chromosome number have an adaptive value and, if so, what this value is. Here we assume that three strategies of genome evolution (shrinkage, expansion, and equilibrium) have developed to find the optimal balance between genomic stability and plasticity. We suggest various modes of DNA double-strand break (DSB) repair in combination with whole-genome duplication (WGD) and dysploid chromosome number alteration to explain the different strategies of genome size and karyotype evolution.

TrendsDespite recent developments in genomics it remains unclear why gene content, chromosome number, and genome size vary independently of each other. Is there a tendency for genome size or chromosome number to increase or decrease over time? Does genome size or chromosome number have an adaptive value and, if so, what is that value?Genomes need a balance between required stability and some degree of variability sufficient for optimal fitness of their carriers.Recent genomic and cytogenomic approaches indicate that, besides sex, whole-genome duplication and erroneous DNA double-strand break repair are the main sources of genome structural variation.This motivated us to elaborate three strategies of genome evolution (shrinkage, expansion, and stasis) between which organisms may switch under the influence of stochastic mutations and/or selection pressure.