Theoretically expected segregation ratios of genotypic and phenotypic classes in the F2 and back-crosses for digenically controlled marker traits linked to the single gametophytic S-locus
1993
Gorenshtejn, N.M.
The methods of genetic analysis in plants with the monogenic gametophytic self-incompatibility system have been developed and presented in this paper. Theoretically expected segregation ratios of genotypic classes in the F2 and back-crosses are calculated for digenically controlled marker traits when only one or both structural loci are linked to the S-locus. The segregation ratios of phenotypic classes for different types of gene interaction (suppression, polymery, complementary genes, etc.) were obtained. It has been shown that the segregation ratios in the F2 depend on the fact, whether plants in the F1 are cis- or transheterozygotes. This is one of many investigated peculiarities of genetic analysis in plants with gametophytic self-incompatibility system. The dependence of the segregation ratios both in the F2 and back-crosses on the frequency of recombinations between the S-locus and structural loci was studied. It has been shown that the expected segregation ratios of genotypic classes are determined unambiguously for different types of gene interaction (except suppression) and the values of recombination coefficients. Therefore, on the basis of two different non-mendelian, segregation ratios in the F2 it is possible to find out the mode of inheritance of a trait under investigation. On the same basis, the coefficients of recombination between structural loci and S-locus can be determined. To analyze the ambiguous situation with a gene-suppressor, an additional information should be used. The segregation ratio in a back-cross (with the parental plant or with its progeny from the forced self-pollination) allows in this case to distinguish between two assumed values of recombination coefficients resulting in the same segregation ratio in the F2
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