Science. 2014 Jan 10;343(6167):193-6. doi:10.1126/science.1245316

Deng Q, Ramsköld D, Reinius B, Sandberg R.

Single-cell RNA-seq reveals dynamic, random monoallelic gene expression in mammalian cells.

“we analyzed mean gene expression levels in cells with biallelic expression and indeed observed them to be 2.0 ± 0.1 times higher [95% confidence interval (CI), bootstrap] than the levels in cells with monoallelic expression at all developmental stages”