The influence of homozygosis in some segments of the maize genome on recombination frequency in the neighbouring ones
--Chernov, AA, Mihailov, ME

The influence of the marker loci of chromosomes 1 (P1), 2 (ws3, lg1, gl2), 6 (y1), 9 (c1, sh1, wx1), 10 (R1) on recombination frequency (rf) in ws3-lg1-gl2 and c1-sh1-wx1 segments was studied. The Ku123 x 2-9m hybrid heterozygous for these loci was used. On 227 F2 plants self-pollinated F3 ears were produced. F3 families were used to estimate genotype of F2 plants for marker loci, and in the suitable F3 families rf values were scored.

Only four significant effects were detected: the influence of the gl2 locus on rf(ws3-lg1), ws3 locus on rf(lg1-gl2), wx1 locus on rf(c1-sh) and c1 locus on rf(sh1-wx1) (see Table 1). The table data show that homozygosis for a marker locus leads to increasing rf value in neighbouring chromosome segments. It may be supposed that meiotic crossing over is suppressed in heterozygous chromosome areas, and the level of this suppression depends on the size of the heterozygous interval (the larger the heterozygous interval the greater the level of suppression).

Table 1. Recombination values (mean rf% ± SE) in the different genotypic classes of F2 (Ku123 x 2-9m).
 
Segment Genotype Number of F3 families analysed Mean rf, % The proportion of the factor in total dispersion
  gl2+/+ 6 20.0±3.3  
ws3-lg1 gl2+/- 64 12.0±0.5 36.6% ***
  gl2-/- 10 21.5±2.1  
  total 80  13.8±0.7  
         
  ws3+/+ 5 25.8±1.5  
lg1-gl2 ws3+/- 64 20.8±0.6 6.9% *
  ws3-/- 2 19.0±1.9  
  total 71 21.1±0.6  
         
  wx1+/+ 13 7.4±0.6  
c1-sh1 wx1+/- 66 5.6±0.3 33.0% ***
  wx1-/- 8 11.8±0.7  
  total 87 6.4±0.3  
         
  c1+/+ 5 28.3±3.2  
sh1-wx1 c1+/- 65 21.6±0.6 10.1% **
  total  87 22.2±0.6  

1) * P<0.05, ** P<0.01, *** P<0.001.

2) genotype for c1 locus in some cases could not be detected because of the interaction with R1 locus.
 


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