Asymmetry of heteropycnosis in tetraploid cells of a grasshopper

In XO male grasshoppers (Acridoidea and Eumastacoidea) X-chromatin is negatively heteropycnotic in spermatogonial mitoses. In neo-XY species which have a fusion between the original X and an autosome it is usual for the former alone to show negative heteropycnosis. This is the case in the Australian Morabine grasshopper species P52a. In tetraploid spermatogonia of this species, however, which contain two neo-X's and two neo-Y's, only one of the neo-X's has a negatively heteropycnotic left limb, the other X having the same degree of condensation as the autosomes. This novel type of behavior is compared with the heteropycnosis of one of the two X's in the somatic cells of female mammals. It is concluded that the asymmetry of condensation of the two X's in tetraploid spermatogonia of P52a demonstrates the existence of a fundamental cellular mechanism which is inherent and only expressed under the abnormal condition of tetraploidy.Supported by Public Health Service Grant GM-07212 from the Division of General Medical Sciences, U.S. National Institutes of Health and by a grant from the Australian Research Grants Committee.