A genome-wide association study, supported by a new chromosome-level genome assembly, suggests sox2 as a main driver of the undifferentiatiated ZZ/ZW sex determination of turbot (Scophthalmus maximus)

•A chromosome-level genome assembly was constructed to disentangle the genetic architecture of turbot SD.•Data suggest that sox2, located within an intron of a long non-coding RNA, is the master SD gene of turbot.•Turbot shows an undifferentiated SD system with evidence of recombination suppression around the SD gene.•Other genomic regions and environmental factors are involved in turbot SD as supported by segregation analysis within families.