Duplications are apparent also at the mRNA level. (a) Data from an experiment comparing mRNA from growing Ax2(Ka) and Ax2(Wee) ordered by chromosomal location, for chromosome 2 only, where Ax2(Wee) has a duplication. This is the only region displaying a striking shift away from log2 ratio = 0. (b) Histogram of log2 ratios within the region duplicated in Ax2(Wee). The distribution tends towards bimodality, with one clear peak near log2 ratio = 0 and a less distinct one towards log2 ratio = 1. Thus, a portion of genes is dosage-insensitive. (c) Correlation between log2 ratios from independent mRNA comparisons. The duplication carried by Ax2(Wee) entirely encompasses the segment duplicated in Ax3 and its derivatives, allowing us to compare the dosage-sensitivity of genes in this overlap in different strains. The data are clearly correlated, with genes sensitive to dosage in Ax2(Wee) tending also to be sensitive in DH1 (unpublished work with T Soldati; the Soldati laboratory strains are indicated by So). A similar set of genes appears to undergo dosage compensation in both strains.