Data from: The origin of a new chromosome in gerbils

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 (Meriones
unguiculatus) 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 (>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.