Fig. 7: Models for chromosome element expression in spermatocytes.
From: Dynamic sex chromosome expression in Drosophila male germ cells
Non-mutually exclusive models. a Gene-level regulation. Movement (green dashed arrow) of genes with male-biased expression (blue ovals) off the X due to deleterious changes resulting from antagonistic selection in females or extinction of genes with male-biased expression on the X, or female-biased expression on the Y (strike through) result in a feminized X and a masculinized Y. X and 4th (red), Y (green), and major autosome (black) chromosomes (elongated bars) shown. b Chromosome-level regulation. This model relies on chromosome-specific regulation, including X-chromosome inactivation. Gene expression depends on chromosome elements that are active (green chromosomes) or repressed (red). Centromeres (Black circles). c Territory-level regulation. In this model the X and 4th chromosomes are restricted to a repressed address (red lozenge) within the nucleus (large circle). This could be the result of a barrier preventing activation of Pol-II or active repression within the territory. The 2nd and 3rd chromosome territories (green lozenges) and the diffuse Y (green lines) are expressed normally. The active nucleolus (n, green circle) is embedded within the repressed domain, but depends on expression of Y rDNA, not X rDNA.
