Mapping studies involving the seedling necrotic mutant, nec2, with dek1, zb4 and p1 have placed nec2 approximately 7 units proximal to dek1 on chromosome 1S. Seeds from the testcross zb4 p1-ww + x (+ p1-wr nec2)/(zb4 p1-ww +) were planted, scored for zb4 and selfed. Each selfed ear was then scored for cob color and a seed sample was planted in the sandbench and scored for nec2. The following data place nec2 approximately 9 units proximal to p1.
Seeds from the testcross, + + x (dek1 +)/(+ nec2), were planted and selfed. The resulting ears were scored for dek1, a seed sample was planted and the seedlings were scored for nec2. The following data were obtained.
As in any testcross involving two lethal mutations, the double mutant class may be under-represented since it requires a crossover in the testcross individual in order to score the presence of both mutants. This appears not to be a major factor in this analysis as both crossover classes were roughly equal and the resulting dek1 to p1 distance of 2 units is in close agreement to the established distance. Nevertheless, the linkage distance may be greater than 7 units.
As reported by Beckett (MNL 49:130), TB-1Sb uncovers nec2 and, thus, the breakpoint of TB-1Sb lies between nec2 and as1.
Dave Hoisington
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