Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Arnel R. Hallauer


The objectives of this study were to: (1) estimate the genetic variances, average levels of dominance, and genetic effects in two maize (Zea mays L.) populations that descended from a high performance single cross, B73 x Mo17, and a related line single cross, B73 x B84; (2) study the relationships between genetic effects and heterosis; and (3) estimate the effects of linkage disequilibrium on the estimates of genetic parameters by using the advanced random mating generations. The parental lines, F1 single crosses, F2 populations of the two F1's and backcross and S1 progenies randomly sampled from each of the F2 and F2 Syn5 populations were evaluated;Heterosis was greater in B73 x Mo17 than in B73 x B84 for yield, ear height, ear length, and ear diameter. In design III and combined design III and S1 analysis, genetic variances estimated for B73 x Mo17 populations were greater than for B73 x B84 populations for yield and other traits. Additive variance for yield estimated for the B73 x Mo17 populations was about two and three times greater than for the B73 x B84 F2 and F2 Syn5 populations, respectively. Estimates of average levels of dominance were in partial to complete dominance range in both populations for all traits;In generation mean analysis, dominance effects were more important in the expression of heterosis for yield and other traits in both B73 x Mo17 and B73 x B84. The greater heterosis observed for yield and other traits in B73 x Mo17 than in B73 x B84 was due to the greater positive dominance effects and smaller negative dominance x dominance effects in B73 x Mo17;Estimates of dominance variance for yield decreased from the F2 to the F2 Syn5 populations for both hybrids. Estimates of additive variance of yield for F2 populations were not significantly different from the estimates for F2 Syn5 populations for both hybrids. This suggested that the effect of coupling and repulsion phase linkages cancelled each other. Linkage also had an important effect on the estimates of epistatic effects of ear height and yield in generation mean analysis for both hybrids.



Digital Repository @ Iowa State University,

Copyright Owner

Geng-Chen Han



Proquest ID


File Format


File Size

106 pages