In the 1987 issue of the Maize News Letter (MNL 61:7-9), we reported on the genetics of a dominant aleurone developmental mutant, Dappled-1 (Dap1), that arose in one of our Mutator stocks. This mutant, which is expressed only in outcrosses as a female, yet is both male and female transmissible, produces a phenotype of irregular patches of normal, pigmented aleurone cells surrounded by colorless and morphologically abnormal aleurone cells. We now present linkage data that suggest that Dap1 is located on the distal half of the long arm of chromosome 5.
During the summer of 1986, we crossed heterozygous Dappled plants by a comprehensive series of waxy translocations. This past summer, we backcrossed the semisterile progeny by a homozygous purple wx R-scm2 line and scored the resultant ears for the Dappled and waxy traits. The only translocations that showed linkage of Dappled with waxy were wx T5-9 (4790) and wx T5-9a (Table 1). The closest linkage (about 3 cM) is with T5-9a, with breakpoints at 5L.69 and 9S.17. Since none of the other waxy translocations (other than T5-9(4790)] showed linkage with dappled, this gene must be located on chromosome 5. The linkage data for T5-9(4790), with breakpoints at 5L.34 and 9L.45, show much looser linkage of Dappled with waxy (about 39 cM), putting Dappled much closer to the T5-9a breakpoint at 5L.69. We are currently making crosses to test linkage of Dappled with pr, v12, yg1, and v2, all on the long arm of chromosome 5.
To date, we have not been able to isolate a homozygous Dappled line. With the use of wx T5-9a, we should be able to place Dappled in close coupling with wx, and use this close coupling to isolate a homozygous wx line that is presumably homozygous for Dappled. Based on our previous unsuccessful attempts to isolate a homozygous Dappled line, we would predict that such a homozygote will be inviable.
Table 1. Translocation backcross data for linkage of Dappled- I with wx T5-9(4790) and wx T5-9a.
Philip S. Stinard
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