Simulation of the Backcross Breeding Method. I. Effects of Heritability and Gene Number on Fixation of Desired Alleles
Reddy, Belum V. S. | Comstock, Ralph E.
The potential of backcross breeding for improvement of a pure line by addition of favorable alleles from a donor line was investigated by computer simulation coupled with quantitative genetics theory. Attention was focused on the effects of heritability (among individual F₂ plants) and of the number of genes of which the allele present in the donor line is more favorable than the one present in the recipient. The specific programs investigated were ones involving a large amount of effort, a minimum of 1,000 pollinations per backcross generation and selection among families in three or more generations. The criterion employed for effectiveness was the probability of fixation in the product of the program of favorable alleles derived from the donor line. Effectiveness was found to be greater when heritability is greater but the effect of increased heritability was not as great as might have been expected. Number of favorable alleles available frcm the donor line had greater impact, particularly when success was defined in terms of probability that all the available favorable alleles would be transferred from donor to recipient. Success, so defined, was limited to one allele in the case of the least laborious of the three programs studied and no more than five in the case of the most costly. On the other hand, when success was measured in terms of percent improvement in the selected trait, it appeared substantial change is possible with heritability as low as 15 percent and favorable alleles available in the range frcm 1 to 16. dditive effects and independent assortment were assumed for genes simulated.
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