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Simulating the Effects of Dominance and Epistasis on Selection Response in the CIMMYT Wheat Breeding Program Using QuCim

^a CIMMYT, Apdo. Postal 6-641, 06600 Mexico, D.F., Mexico
^b School of Land and Food Sciences, The Univ. of Queensland, Brisbane, Qld 4072, Australia
^c Pioneer Hi-Bred International Inc., 7250 N.W. 62nd Avenue, PO Box 552, Johnston, IA 50131, USA

View larger version (25K): [in a new window]   Fig. 1. Data structure to define breeding strategies in QuCim.

View larger version (35K): [in a new window]   Fig. 2. Germplasm flow in the Selected Bulk selection method used in CIMMYT's wheat breeding program.

View larger version (16K): [in a new window]   Fig. 3. Two kinds of pleiotropic effects exemplified by the pleiotropic effects of grains per spike on lodging and kernel weight.

View larger version (67K): [in a new window]   Fig. 4. Four genetic models used to investigate the effects of dominance and digenic epistasis on selection. 1, 2, 3, and 4 represent the four genetic models, i.e., pure additive yield genes (AD0), partial dominance yield genes (AD1), partial or overdominance yield genes (AD2), and digenic epistasis yield genes (ADE); Column a shows the three genotypic values on each of 20 yield genes for Models AD0, AD1, and AD2, and the gene 1 and gene 2 interaction for Model ADE; Column b shows the percentage of genetic variance explained by each gene or each epistasis network. All genes have the same frequency, 0.5, in the reference population used to estimate the genetic variation. Variation from pleiotropic genes was excluded. A and a are the two alleles on each locus. A and a, and B and b are the alleles on the two interacting loci.

View larger version (47K): [in a new window]   Fig. 5. Effect on genetic advance. 1a, 1b, and 1c: Advances on yield in the Cd. Obregon environment type for the three initial populations identified by gene frequencies 0.1, 0.5, and 0.9, respectively; 2a, 2b, and 2c: Advances in yield in the Toluca environment type for the three initial populations; 3a, 3b, and 3c: Advances on lodging, stem rust, heading and kernel weight in the Cd. Obregon environment type for the three initial populations.

View larger version (50K): [in a new window]   Fig. 6. Gene frequency in the final selected population following 10 cycles of selection. 1, 2, and 3 represent the three genetic models, i.e., partial dominance yield genes (AD1), partial or overdominance yield genes (AD2), and digenic epistasis yield genes (ADE); a, b, and c correspond to the three initial populations identified by gene frequencies 0.1, 0.5 and 0.9, respectively.

View larger version (54K): [in a new window]   Fig. 7. Changes in variance components following selection. 1, 2, 3, and 4 represent the four genetic models, i.e., pure additive yield genes (AD0), partial dominance yield genes (AD1), partial or overdominance yield genes (AD2), and digenic epistasis yield genes (ADE); a, b, and c correspond to the three initial populations identified by gene frequencies 0.1, 0.5, and 0.9, respectively.

View larger version (22K): [in a new window]   Fig. 8. The effect of linkage phase and degree on response to selection.