Degree Type


Date of Award


Degree Name

Doctor of Philosophy




Two experiments were conducted to evaluate the effects of random mating in the F(,2) of four single crosses of maize (Zea mays L.): B73 x Mo17 (unrelated parents), B73 x B84 (related parents), and B73 x B79 and B77 x Mo17 (intermediate parent relation). The objective of the first experiment was to estimate the change in means over six generations of random mating. S(,1) progenies were derived in the F(,2) and F(,2)Syn5 generations of B73 x Mo17 and B73 x B84 (second experiment) to estimate the changes in genetic variances and traits associations of 14 traits due to random mating.;Changes in means were not expected with random mating under the assumption of no epistasis. There were some small changes in the means of the four single crosses, measured by the regression coefficient for grain yield and grain moisture, that were attributed to either natural selection or epistatic effects.;There were some instances in B73 x Mo17 where the genetic variability was reduced significantly, suggesting that coupling linkage phase was predominant in those traits. The estimates of genetic variances in B73 x B84 increased significantly for some traits, which suggests that repulsion linkage phase was predominant. No significant change was observed for grain yield in the B73 x Mo17 cross. The range of variability was not increased for most traits. The changes in genetic variances suggested that recombination was enhanced and were attributed to either changes in linkage disequilibrium or changes in allelic frequency that occurred during the generations of random mating. The range of segregation was higher in the B73 x Mo17 cross.;There were some significant changes in the genetic correlation coefficients of trait associations in B73 x Mo17 and B73 x B84 single crosses; a higher proportion of changes were observed in the B73 x Mo17 cross. On the average, the genetic correlation between traits was increased significantly in 64% of trait associations. Some changes in the correlation between grain yield and some traits were observed in B73 x Mo17, but no change was observed in B73 x B84. Insufficient evidence was obtained to support the use of random mating in F(,2) populations from crosses of inbred lines to increase genetic variation.



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Jorge Covarrubias-Prieto



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178 pages