Looking for mutations affecting crossing over

The recovery of parental gametes in homozygous stage from selfed F1 hybrids, giving directly a number of inbred lines, is supposed to result from association of a general suppression of crossing over and a directional segregation of parental gametes (Oenothera method imagined by Burnham, 1946). A preliminary search for a suppression of crossing-over other than an inversion system was carried out for the fl2 su1 region located on the fourth chromosome. The need for a large screening was found using kernel traits according to the following procedure.

Eighty-five flint local varieties were crossed in an isolated field with a homozygous strain for fl2 and su1 as a male parent in 1978. The F1 plants were detasseled in 1979 and pollinated in an isolated field by a su1 strain. Therefore the ears were screened for their lack of floury kernels, which are recombinants:
 
  Female Gametes Kernel Genotypes Pheno-
types
Par. fl2 fl2 su1 su1 fl2 fl2 + su1 su1 su1 su1
Par. + + + + + + + + + su1 +
Rec. fl2 fl2 + + fl2 fl2 + + + su1 fl2
Rec. + + su1 su1 + + + su1 su1 su1 su1

Among 15,000 screened ears, only one desirable ear with normal and sugary kernels was found in the population of Barisis (Aisne) France. In order to eliminate the possibility of an inversion (the collected ear was not well filled), or a reverse mutation in 1978 in the pollen (fl2 to +), the plants from sugary kernels will be pollinated by a normal type. All kernels should have a floury 2 appearance if we have detected a new system of suppression of crossing over. In case of success, we will have to check this system for other regions and chromosomes.

M. Pollacsek


Please Note: Notes submitted to the Maize Genetics Cooperation Newsletter may be cited only with consent of the authors.

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