C-Im857059 was uncovered in an isolation plot containing the cross C-I Sh Bz Wx/C-I Sh Bz Wx En x C sh bz wx/C sh bz wx. This mutant is unstable and has an I insert that is under the control of En. This was proved in several ways but one example will be given. Sectored kernels were crossed by a tester containing c2-m2 and wx-m8, alleles responsive to En or Spm, C-Im Sh Bz Wx/C sh bz wx X c2-m2 wx-m8, and sectored kernels obtained from this cross were again crossed by c2-m2 wx-m8. Colored, sectored pale, and colorless kernels are obtained among the progeny and are tested for the wx phenotype. The wx mutability is from wx-m8 with En.
The colored are from the C Sh Bz wx-m8 chromosome The sectored and pales are from the other chromosome (C-I Sh Bz Wx) with the wx phenotypes arising from crossovers. All the sectored show wx mutability; none of the pales show wx-mutability (Table 1).
The conclusion from this analysis is that the pales represent the C-Im(r) allele without En. The sectored are the same allele with En. Thus, the pales are suppressed somewhat in their color-suppressive capacity and these represent an I insert in the C-I allele responding to En but not completely abolishing the suppressive effect of C-I In summary,
Pale = C-Im(r)/C no En (none show wx-mutability)
Sectored = C-Im(r)/C En (Excisions release the modification of the color suppressing potential); all show wx-mutability.
Colorless = C-Im(r)/C-I-m(r) ± En
Table 1. Test of En control of C-I-m857059. Progeny types from cross tested for En presence with the wx-m8 allele.
Peter A. Peterson
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