Data from: The origin of a new chromosome in gerbils

<p><span>Gerbil genomes have both an extensive set of GC-rich genes and chromosomes strikingly enriched for constitutive heterochromatin. We sought to determine if there was a link between these two phenomena and found that the two heterochromatic chromosomes of the Mongolian gerbil (<em>Meriones unguiculatus</em>) have distinct underpinnings: chromosome 5 has a large block of intra-arm heterochromatin as the result of a massive expansion of centromeric repeats (probably due to centromeric drive); while chromosome 13 is comprised of extremely large (&gt;150kb) repeated sequences. We suggest that chromosome 13 originated when a functionally important 'seed' broke off from another chromosome and underwent multiple breakage-fusion-bridge cycles. Genes with the most extreme GC skew are encoded on this chromosome, most likely due to the restriction of recombination to a narrow permissive region (since GC bias is linked with recombination-associated processes). Our results demonstrate the importance of including karyotypic features such as chromosome number and the locations of centromeres in the interpretation of genome sequence data, and highlight novel patterns involved in the evolution of chromosomes.</span></p>