We sampled 16 wild lake char (Salvelinus umbla) and used their gametes to investigate the genetic consequences of different mating scenarios. A full-factorial breeding was used to separate additive genetic from maternal environmental effects, and embryos were raised singly after sublethal exposures to a pathogen, a common pollutant, or water only. In all treatment groups, embryo development was strongly reduced with increased genetic relatedness between the parents. Contrary to predictions of ‘good genes’ sexual selection,...