The question of the order of the genes Bf1 and bm4 at the tip of the long arm of chromosome 9 is an important one for those studying deletions and other cytological phenomena on 9L. To date, the placement of the order of Bf1 and bm4 has been based on the compilation of two-point linkage data. No direct three-point tests have been reported. This report summarizes the results of a three-point linkage test between Wc1, Bf1, and bm4 that confirms the current order on the maize linkage map of chromosome 9.
Table 1. Three-point linkage data for Wc1 Bf1 bm4.
Testcross: (Wc1 bf1 Bm4 / wc1 Bf1
bm4)
X wc1 bf1 bm4
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% recombination wc1 - bf1 = 10.9 + 1.7
% recombination bf1 - bm4 = 4.4 + 1.1
The linkage test was set up as a testcross as indicated in Table 1. Kernels from the testcross ear were planted in the field and the resulting plants were self-pollinated. Mature plants were scored for bm4 within a few days after pollination. The self-pollinated ears were scored for Wc1. Approximately 40 kernels from each ear were grown to seedling stage in a sand bench, and the seedlings were scored for Bf1 using a UV light. The following linkage relationships were established (distances are given in centimorgans): Wc1 - 10.9 - Bf1 - 4.4 - bm4. These data confirm the order of these three genes on chromosome 9, but the distance between Wc1 and Bf1 is much less than that reported on the current linkage map (30 centimorgans, based on the data of Burnham, MNL 33:74, 1959). The data of Coe (MNL 38:109, 1964 and MNL 61:47, 1987), which give a Wc1 - Bf1 distance of 16 centimorgans, are more consistent with the data presented in this report.
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