AMES, IOWA
Iowa State University

Mutables at in
--Peter A. Peterson

in-m918732-13. This is an early sectoring in-mutable. It arose in an En/Spm isolation plot. In the cross c2/c2 in-o/in-o x c2/c2 in-m/in-o the following segregation ratio was observed.
 
pale pale cl-areas cl Total
86 199 175 460

Whereas the pale class is expected to be 50%, it is seriously deficient. Such a ratio arising from male transmission has the earmarks of a gamete factor, though none have been reported in chromosome 7. This aspect will be pursued.

in-m918732-14. This in-mutable arose in a plot containing En/Spm. The mutability pattern shows heavy (early) colorless sectors on a pale colored background from the cross c2 c2 in-m/- x c2 c2 in in. The following segregation was observed. The in-m parent would be homozygous or heterozygous.
 
pale pale cl-sectors cl Total
92 0236-3/0336 133 71 15 219
92 0236-5/0301 58 126 53 237

Plant -3 could be heterozygous. Plant -5 could be homozygous with a high incidence of changes to pale (non-mutable) and colorless via excisions. The sectors for this mutable allele are early-occurring.
in-m918732-4. This mutable in-m arose in an En/Spm plot. In a confirming cross c2/c2 in-m/in-o x c2/c2 in-o/in-o, the following segregation was seen.
 
pale pale-cl areas cl Total
92 1201y-21/0528 88 59 35 171

The high frequency of colorless (cl) indicates a high rate of revertants, which agrees with the pattern of mutability showing early colorless areas.

in-m918732-19. This in-mutable arose in an En/Spm isolation plot. From a self of c2/c2 in-m/in-o, kernels with colorless sectors on a pale background were selected. In the cross c2/c2 in-o/in-o x c2/c2 in-m/in-o the following segregation was observed.
 
pale pale-cl areas cl Total
92 0303/0245-9t 1 122 90 213

The segregation indicates that plant -9t was homozygous in-m/in-m and would appear to be autonomously mutable (lack of pale segregants). The high frequency of colorless (cl) is likely due to revertants but must be tested.

There are approximately 35 other in-mutables that are currently being confirmed. All came from an En/Spm containing plot. Though all contain and show an En, none has been confirmed as to a system in a strict co-segregation test. There has been a crucial lack of a confirmed usable reporter allele for En but this is now corrected. 


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