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Abstract

We are only beginning to incorporate non-additive effects into our understanding of complex traits such as growth. F1 hybrids provide a facile means for comparing between additivity and non-additivity by creating many novel allele combinations and interactions. We studied the transcriptome of 141 random crosses of Arabidopsis thaliana, and found additivity to be rare, consistently observed for only about 300 genes enriched for roles in stress response. Rare- allele burden affects the expression level of these genes but not F1 growth. Non-additive gene expression, especially at below parental average level, is in comparison much more common. Rare-allele burden in this set, unlike in the additive ones, is strongly correlated with F1 growth. This underscores under-dominance as the predominant driver of emergent behavior of rosette growth in A. thaliana F1 hybrids, laying the foundation for understanding molecular mechanisms and evolutionary forces that lead to dominance complementation.