9/13 As a concrete example, one genome-wide significant dominance effect on HbA1c levels is in the body of the ZFP92 gene, which encodes for zinc finger protein that regulates DNA transcription and transposable element silencing and may plausibly influence X chromosome inactivation.

8/13 In trying to make sense of dominance signals and Xi specifically, we formalized a simple expectation for dominance effects that is unique to X-linked variants: a variant will produce a dominance effect on a trait if it is also linked to a QTL for X chromosome inactivation.

7/13 The significance of additive allelic effects grows with Xi expression levels. Critically, dominance signals (when alleles bias which X is inactivated) also track Xi escape in several traits, including lymphocyte %, HbA1c, and schizophrenia.

4/13 We were taken back by how predictive Xi expression levels were for sex differences and variation within females. In particular, Xi expression was a strong linear predictor of female–male expression difference across non‐pseudoautosomal (NPX) genes.