ΔWS profiles. ΔWS = [(A+T)-(G+C)]/(A+T+G+C) is plotted on the y axis, at each position x. (A) Differences between the ΔWS profiles for human gene groups with narrow, medium, and wide expression can be observed. The significance thereof is assessed (see text and Figure 7). (B) For the orthologous genes in Fugu, there are no observable differences. (C) For narrow and wide expression groups in Drosophila, only small differences are present.