Plant genera <i>Cannabis</i> and <i>Humulus</i> share the same pair of well‐differentiated sex chromosomes

We recently described, in Cannabis sativa, the oldest sex chromosome system documented so far plants (12–28 Myr old). Based on estimated age, we predicted that it should be shared by its sister genus Humulus, which is known also to possess XY chromosomes. Here, used transcriptome sequencing of an F1 family H. lupulus identify and study chromosomes this species using probabilistic method SEX-DETector. identified 265 sex-linked genes lupulus, preferentially mapped C. sativa X chromosome. Using phylogenies genes, showed a region had already stopped recombining ancestor both species. Furthermore, as Y-linked gene expression reduction correlated position chromosome, highly Y degenerated dosage compensation. report, for first time Angiosperms, two different genera. Thus, recombination suppression started at least 21–25 ago, then (either gradually or step-wise) spread large part (c. 70%), leading