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Comments on Wood WB et al. (1985) Worm Breeder's Gazette "suppression of dpy-22 male inviability by X duplications." (0)
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Wood WB, & Meneely PM (1985). suppression of dpy-22 male inviability by X duplications. Worm Breeder's Gazette, 9(1), 71. Unpublished information; cite only with author permission.
XO males carrying the dpy-22(e652) X mutation generally do not survive to adulthood; those that do are small and sickly. We have postulated that the low viability is due to apparent under-expression of the X chromosome caused by this mutation (Meneely and Wood, 1985 C. elegans Meeting Abstracts, p. 90; Meneely et al., in preparation). Presence of X duplications generally appears to increase overall X expression (Meneely and Wood, 1983, Genetics 106:29; Meneely, this issue). To determine how these two effects interact, we have begun testing the viability of dpy-22 XO males that carry X duplications derived from either the maternal or the paternal parent. In N2(male) x dpy-22(hermaphrodite) crosses, the progeny male ratio (PMR: identifiable Dpy progeny males to total outcross progeny) ranges from about 10% to 30%. For the initial duplication experiments we used mnDp25 (X;I), a duplication of about 25% of the X including the unc-3 locus but not the dpy-22 locus. The cross mnDp25/+;unc-3/0(male) x dpy-22 rodite) gave PMR of 16% +- 5% (39/244 in two experiments), compared to 19% +- 6% (31/165) in the control cross N2(male) x dpy-22 maphrodite). Therefore, introduction of this duplication paternally has no significant effect. To test the effect of introducing it maternally, we crossed N2(male) x mnDp25;unc-20 unc-3(hermaphrodite) (rather than the simpler mnDp25;dpy-22 maphrodite), which turned out to have unexpectedly low viability). We obtained a PMR of 46% +- 5% (158/341), compared to 5% +- 2% (21/389) in the control cross N2( male) x unc-20 unc-3(hermaphrodite). Similar results have been obtained in preliminary experiments with mnDp8 (-15% of X) and mnDp9 (-25% of X), neither of which include the dpy-22 locus. Further experiments with these and additional duplications are in progress. So far it appears that X duplications not including the dpy- 22 locus can suppress the inviability of dpy-22 XO males if supplied from the maternal parent, but not if supplied from the paternal parent, consistent with a maternal effect of X duplications on early X- chromosome expression in the embryo.