Figure 4

Parameters of bimodal transcription abundance classes in Drosophila by population. (a, b) Histograms of magnitude of differences between modes of the two transcript abundance classes (TACs), on a log base-2 scale, in North Carolina (NC) and California (CA), respectively. In both populations the median difference is between 1.5-fold and 2-fold, but a few transcripts exhibit differences as great as 16-fold. (c) Histograms of observed (solid bars) and inferred (open bars) minor TAC frequencies in the NC sample. (d) Histogram of observed distribution of minor TAC frequencies in the CA sample, relative to expected minor single nucleotide polymorphism frequencies under the Ewens sampling distribution, with the population parameter θ (that is, 4Nμ) equalling 0.05 (red line), 0.10 (blue line), or 0.20. The two curves for the most part lie within the range of expected values for D. melanogaster defined by the red and blue curves, although there is a slight excess of minor transcript frequencies between 5% and 10%.