SUMMARYThe major genes for dwarfism in Norm 10 wheat, Rht 1 and Rht 2 are located on chromosomes 4A and 4D. The gene for extreme dwarfness from Tom Thumb, Rht 3, is located close to, or is allelic with Rht 1 on chromosome 4A. An F2 telocentric mapping technique has been employed to locate these genes by using their gibberellin insensitive phenotype. Gai/Rht 1 and Gai/Rht 3 were estimated to be 13 map units from the centromere on the arm of chromosome 4A and Gai/Rht 2 15 map units from the centromere on the long arm of chromosome 4D. These results suggest that the genes are part of a homoeoallelic series.
SUMMARYThe relative efficiencies of the use of backcross and F2 families for telocentric chromosome mapping in wheat are compared in three dominance situations. The effects of differential transmission of the telocentric and of differential zygotic viability are considered. Analysis of selfed progeny may be more complex but selfing will often be more convenient and in several genetic situations will be preferable to the more usual backcross technique.
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