In the last gazette we reported on the genetic mapping of spontaneously derived chromosome I duplications. Since this time, one of us (RER) has re-evaluated the complementation data and has proposed a more parsimonious map. In addition,
unc-38 is now in a new position based on some data from this lab and from P. Mains (personal communication). The maps in Figures 1 and 2 summarize the new interpretations. The h duplications 26, 27, 30 and 59 are spontaneous
unc-63(-) derivatives of hDp23. hDp23 was itself a spontaneous duplication derived from hDp7. hDp78 is a spontaneous derivative of hDp4. Since the last note, a new
dpy5(-) derivative of hDp74, hDp100, was isolated in the lab by Shiv Prasad (Figure 1). In the old map, the gene order was
let-375 let-359 (
let-364 unc-63) (
let-361 let-371 spe-11). According to the new interpretation, the gene order is
let-375 (
let-364 unc-63)
let-359 spe-11(
let-361 let-371) (Figure 2). [See Figure 1] All the spontaneous Dps (indicated in Figures 1 and 2 by an asterisk) are characterized by double, and sometimes triple, deletion events. The deletions often involve both ends of the progenitor duplications. For example, hDp30 results from a deletion of hDp23 involving both the
dpy-14,
unc-63 and
let-363 regions. In the previous article we proposed a structure for hDp4 based on the structure of its derivative hDp78; which has deletions of the
dpy-14,
unc-57 and
let-363 regions. The proposed structure for hDp4 is shown in Figure 3a and involves a ring chromosome with a superimposed inversion relative to the linear map. With the revised map shown here, we can now propose a similar structure for hDp23, and possibly hDp74, based on the structure of their derivatives. If hDp23, like the proposal for hDp4, is a ring chromosome with a superimposed inversions than the multiple deletions with respect to the linear map can be explained by a single deletion on the ring chromosome-inversion map. Figure 3b shows the proposed structure for hDp23 and the deletions which produced the four derivatives. [See Figures 2-3]