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.