Figure 1.—

Expression of the fourth chromosome is reduced in roX1 roX2 males. (A) In roX1 roX2 males the expression of fourth-linked genes (blue) decreases in comparison with the rest of the genome (gray). Points represent the log₂ of the ratio of gene expression in roX1^SMC17AroX2 males to control males (roX2) plotted against expression level (log₂ absorbance). Numbers and types of genes plotted are 9880 nonfourth-linked genes and 74 fourth-linked genes. (B) The density distribution of log₂ expression (mutant/control) for fourth-linked genes (blue) and second and third chromosome genes (gray) in males. The distribution of fourth-linked genes differs significantly from the remaining autosomal genes (adjusted P-value < 6.6 × 10⁻¹⁶; Wilcoxon test). (C) In roX1 roX2 females the expression of fourth-linked genes (blue) is unchanged. The rest of the genome is shown in gray. Data is presented as the log₂ of the ratio of gene expression in roX1^SMC17AroX2 females to control females (roX1^SMC17AroX2; [w⁺Hs83- roX1⁺]) plotted against expression level (log₂ absorbance). Genes contributed to this analysis are 8433 nonfourth-linked and 69 fourth-linked genes. (D) The density distribution of log₂ expression (mutant/control) for fourth-linked genes (blue) and second and third chromosome genes (gray) in female larvae. The distribution of fourth-linked genes is not significantly different from that of the second and third chromosomes (adjusted P-value 0.92). Only genes present in at least two out of three replicates were included. See File S1 for details of microarray hybridization and analysis.