I am using tweeDEseq to look at differential expression between two genotypes. I would like to compare genotypes using litter as a covariate using tweeDEglm; however, I am having trouble implementing this. 

Would this be the correct approach to compare genotype using litter as a covariate?

> resPTglm <- tweeDEglm(~litter + genotype, counts = countData)

Thanks!