RT Journal Article SR Electronic T1 The X chromosome of the German cockroach, Blattella germanica, is homologous to a fly X chromosome despite 400 million years divergence JF bioRxiv FD Cold Spring Harbor Laboratory SP 279737 DO 10.1101/279737 A1 Richard P. Meisel A1 Judith R. Wexler YR 2018 UL http://biorxiv.org/content/early/2018/03/10/279737.abstract AB The chromosomes that are sex-linked can differ between closely related species. Cases of long-term conservation could be informative of factors that prevent this sex chromosome turnover. We analyzed whole genome sequence data and found that many of the same genes are on the German cockroach, Blattella germanica, X chromosome and the ancestral X chromosome of higher flies. We also show that three regulators of transcription and chromatin on the fly X chromosome are conserved in the cockroach genome. We hypothesize that the common ancestor of cockroaches and flies had an X chromosome that resembled the extant cockroach/fly X. Cockroaches and flies diverged ∼400 million years ago, making this the longest documented conservation of a sex chromosome. Cockroaches and most flies have different mechanisms of sex determination, suggesting long-term conservation of the X chromosome despite evolution of the sex determination pathway.