Phases of sex chromosome inactivation in oncopeltus fasciatus and pyrrhocoris apterus (Insecta, Heteroptera)

Sex chromosomes in Oncopeltus fasciatus and Pyrrhocoris apterus are heterochromatic and transcriptionally inactive in well-defined phases of development. In Oncopeltus, which has the XX/XY type of sex determination, the Y-chromosome seems to be inactive in aE tissues. The X-chromosome is inactivated during the last spermatogonial division and remains so throughout spermatogenesis. The X-chromosome of Pyrrhocoris, which is of the XX/XO type of sex determination is inactive in the same stages as that of Oncopeltus and during an additional phase in early oogenesis. X inactivation in spermatogenesis is interpreted as a form of gross regulation of gene activity on the chromosomal level.