Extrinsic gene-expression noise
= Extrinsic gene-expression noise
{title2=$\eta_{\rm ext}^2=\langle xy\rangle-1$}
Expression fluctuations caused by shared variation in cellular conditions, such as expression machinery or growth state. Matched reporters tend to co-vary. For mean-normalized reporters whose intrinsic components are conditionally independent, the squared extrinsic noise equals $\langle xy\rangle-1$.