Cultured cells homozygous for a mutation show a significantly different phenotype from cells homozygous for the wild type allele. Both have normal standard deviations. However, when I measure the same phenotype in cells heterozygous for the mutation, the mean is as expected between both measurements, but the standard deviation increases to +/- 40-50%. What could be the reason? Is it possible that the cells express different ratios of both alleles although they have the same genetic background?
I don't have an answer, but I admire the problem :)
No, honestly, your observation seems to be very interesting biologically. One could speculate that the cells decide which allel to activate, so that some activate the wt and others the mut allele. This would lead to a bimodal distribution if you look at a single-cell level (-> suggestion to do a suited experiment). However, when looking in larger population of cells (culture) one would expect the effect to "average out" ... unless the cultures start with relatively few cells that grow and divide and inherit the activation of one of the alleles (epigenetics?) or the cells communicate and influence each other (parakrine effects? cuorum sensing?). All biologically very interesting questions: is an allel "selected"? by what mechanism? is the activation inherited? how? ...
Caveat: I am not an expert in allele-specific gene-activation and it might be that all this is already studied and well known. And before starting to do many experiments in this direction I would anyway not only serch the literature but also cross check if the difference in the variability is reliable. Have you had enough data to get a sufficiently precise estimate of the variance so that you can recognize a 40% difference in SD with sufficient confidence? Have you replicated the whole experiment to confirm your findings?
Thank you for your answer!
Well, so far this data is preliminary. I just became curious because I observed this effect with different phenotypes of my cell line (neither prepared with the same batch, nor on the same day)... and hoped that there is maybe a simple explanation that I overlooked so far.
Actually, I checked now the distribution of this data, expecting two peaks for the cell groups expressing the wt and mut allele or one for an intermediate value, but it looks rather like a shift towards the mut phenotype with a small range of cells showing values in and above the wt range. Maybe really just some of them are reprogrammed for a so far unknown reason. Let's see if this pattern persists in the repetitions...
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