The hidden complexity of Mendelian traits across yeast natural populations. Genetic complexity traits

Heritable traits are determined by genetic factors, and the inheritance patterns depend on the underlying complexity. To date, global landscape of the genetic complexity of traits across natural populations is unknown. Using Saccharomyces cerevisiae natural isolates, we analyzed the offspring fitness distribution and segregation patterns for various stress responsive traits across a large number of crosses, and showed that most traits are complex (82.6%, 727/880), resulting from both additive and epistatic variants. By contrast, monogenic Mendelian traits are rare, representing 9.8% (86/880). Further tracing of the effect of a causal allele across multiple genetic backgrounds revealed the hidden complexity of Mendelian traits, where significant deviations from Mendelian inheritance expectation was observed in 30% of the cases. Our data provided the first precise estimation of the relative proportion of Mendelian traits, and illustrated the extent to which different genetic background could impact the genetic complexity of traits across a yeast population.