Three cycles of recurrent selection for altered recombination frequency in maize
The variability among progeny in a plant breeding population depends on the amount of recombination that occurs in meiosis preceding selection. The recombination arises either from the independent assortment of chromosomes or from crossing over during chromosome synapsis. Crossing over is not a constant value; it differs based on background genotype. This research determined the effectiveness of three cycles of recurrent selection for increased or decreased crossing over in Zea mays L. Testcrosses measured male recombination frequency on three chromosomes: 4, su1-c2; 5, a2-bt1-pr1; and 9, sh1-bz1-wx1. Sixty plants from each of three populations (cycle 0 [C0], cycle 3 high recombination [C3HR], and cycle 3 low recombination [C3LR]) were evaluated. The mean recombination frequency changes between C0 and C3HR are significant at all chromosome regions (su1-c2, +5%; a2-pr1, +24%; sh1-wx1, +8%). The mean recombination frequency changes between C0 and C3LR are significant at the chromosome 4 (su1-c2,-15%) and 5 (a2-pr1,-27%) linkage groups. The mean recombination frequency did not change significantly from C0 to C3LR at either of the chromosome 9 regions. Compared to the C0 population, the sum of the genetic distances at these chromosome regions increased 9.5% in the C3HR population and decreased 14.9% in the C3LR population. Selection for high or low recombination frequency successfully modified recombination frequency.