In many species with sex chromosomes, the Y is a tiny chromosome. However, the dioecious plant has a giant ~550-megabase Y chromosome, which has remained unsequenced so far. We used a long- and short-read hybrid approach to obtain a high-quality male genome. Comparative analysis of the sex chromosomes with their homologs in outgroups showed that the Y is highly rearranged and degenerated. Recombination suppression between X and Y extended in several steps and triggered a massive accumulation of repeats on the Y as well as in the nonrecombining pericentromeric region of the X, leading to giant sex chromosomes. Using sex phenotype mutants, we identified candidate sex-determining genes on the Y in locations consistent with their favoring recombination suppression events 11 and 5 million years ago.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC11890086PMC
http://dx.doi.org/10.1126/science.adj7430DOI Listing

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