[R-sig-ME] GLM for comparing relative growth rates under different conditions

[Daniel Rubi]

Hi,I have this experimental design: I have two sets of cell lines. One in which I mutated a gene and another in which I didn't and therefore serves as the control. I grow each of these cell lines under two conditions - one is selective and the other is normal and is therefore the control.What I'm measuring is a proxy for the number of cells after 100 hours - the end of the experiment, which is not an integer but rather a float. Since I start the experiment with the same number of cells for both cell lines and both conditions, this is assumed to be a proxy for growth rate.I'd like to estimate the effect of the genotype (gene mutated or gene normal) on growth under the selective condition relative to the normal condition. In simple words, is the ratio of the proxy of the number of cells from the mutated cell line under the selective condition to the proxy of the number of cells from the mutated line under the normal condition different from the ratio of the non-mutated cell line under selective and normal conditions?I have 6 replicates of each cell line in each of the conditions. I cannot assume that the ratios are in the [0,1] range and therefore a beta regression is not likely to fit here.Also, none of the four groups (2 cell lines in 2 conditions) are paired in any way.What would be the appropriate GLM for this problem?

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