What it is
Synteny blocks are stretches of chromosome in which the order of genes or sequences is shared between two species' genomes, and they break up as genomes are rearranged over evolution. The authors formalize three models of genome evolution that yield analytical distributions of synteny block sizes between pairs of genomes: the random breakage model, with breakpoints distributed uniformly; the fragile breakage model, with breakpoint hotspots; and what they term the correlated breakage model, with pairs of nearby breakpoints. Fitting these theoretical distributions to the empirical ones from a comparative analysis of nearly 200 mammalian genomes, they find that the fragile and correlated breakage models are far more consistent with mammalian genome evolution than the random breakage model. The parameters inferred for each model qualitatively agree with previously calculated rates of mammalian genome evolution. Because the fragile and correlated models perform comparably with each other, the authors suggest that either could serve as an improved null model of genome evolution for statistical tests that look for syntenic regions unlikely to exist by chance.
Why it matters
Fitted to nearly 200 mammalian genomes, models with breakpoint hotspots or paired nearby breakpoints describe synteny decay far better than one of uniformly random breaks. Synteny blocks, the stretches where gene order is shared between species, break up as genomes rearrange, and tests for conserved regions need a baseline for which shared regions could arise by chance. Because the fragile and correlated breakage models fit comparably, the authors suggest either could serve as an improved null model for statistical tests that look for syntenic regions unlikely to exist by chance.
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Filed underGenome Rearrangement Algorithms, Chromosomal and Genetic Variations, Genomic variations and chromosomal abnormalities