Heterochiasmy and the establishment of gsdf as a novel sex determining gene in Atlantic halibut
Rolf B. Edvardsen, Ola Wallerman, Tomasz Furmanek, Lene Kleppe, Patric Jern, Andreas Wållberg, Erik Kjærner‐Semb, Stig Mæhle, Sara Olausson, Elisabeth Sundström, Torstein Harboe, Ragnfrid Mangor-Jensen, Margareth Møgster, Prescilla Perrichon, Birgitta Norberg, Carl‐Johan Rubin
Abstract
Atlantic Halibut (Hippoglossus hippoglossus) has a X/Y genetic sex determination system, but the sex determining factor is not known. We produced a high-quality genome assembly from a male and identified parts of chromosome 13 as the Y chromosome due to sequence divergence between sexes and segregation of sex genotypes in pedigrees. Linkage analysis revealed that all chromosomes exhibit heterochiasmy, i.e. male-only and female-only meiotic recombination regions (MRR/FRR). We show that FRR/MRR intervals differ in nucleotide diversity and repeat class content and that this is true also for other Pleuronectidae species. We further show that remnants of a Gypsy-like transposable element insertion on chr13 promotes early male specific expression of gonadal somatic cell derived factor (gsdf). Less than 4.5 MYA, this male-determining element evolved on an autosomal FRR segment featuring pre-existing male meiotic recombination barriers, thereby creating a Y chromosome. Our findings indicate that heterochiasmy may facilitate the evolution of genetic sex determination systems relying on linkage of sexually antagonistic loci to a sex-determining factor.