<p>Is there a software package for GWASs that can include an interaction effect (SNP x predictor) in the regression using dosage data?</p>

Can you use [PLINK2](https://www.cog-genomics.org/plink2/assoc#linear)?

That provides an interaction term for the linear regression... In terms of the dosage data, do you have to use the probabilistic data, or would best-guess hard-calling work?