Degree Type


Date of Award


Degree Name

Doctor of Philosophy



First Advisor

Arnel R. Hallauer


Linkage disequilibrium may cause bias in estimates of additive and dominance variances ([sigma]spA2 and [sigma]spD2) and the average level of dominance ([bar] d) in maize (Zea mays L.) F2 populations. The effects of linkage disequilibrium are studied by comparing genetic parameter estimates of random mated F2 populations with estimates from their base F2. Relatively few experiments of this type have been conducted, but the results consistently indicate that [sigma]spD2 and ![bar] d are overestimated in F2 populations, particularly for yield. These studies suggest that genes expressing partial to complete dominance are of primary importance in the expression of heterosis for yield. F2 populations derived from elite inbred lines which express superior heterosis in hybrid combination have not been evaluated previously. A B73 x Mo17 F2Syn10 population was generated by random mating the F2 population for 10 generations. Estimates of genetic parameters of the B73 x Mo17 F2 and F2Syn10 were compared. Estimates of [sigma]spD2 were generally smaller in the F2Syn10 population than in the F2, although the differences were not significant for the traits evaluated. The difference was particularly large for yield, with a 60 percent reduction of [sigma]spD2 in the F2Syn10 relative to the F2. The average level of of dominance ( ![bar] d) for yield decreased from 1.17 in the F2 to 0.80 in the F2Syn10. Evidence for overdominant gene action in the elite B73 x Mo17 F2 population was no greater than in non-elite populations studied previously. Genes expressing partial dominance appear to be the predominant cause of heterosis expression for yield in this population. Estimates of ![bar] d for other traits did not exceed 1.0 in either population. Additive variance for yield decreased slightly in the F2Syn10, but increased substantially for plant and ear heights relative to the F2. Means of the F2 and F2Syn10 were statistically different only for percent grain moisture and ear height. Estimates of heritability varied little between the populations for the traits tested. Consistent trends of genetic and phenotypic correlations of traits were not observed between the populations.



Digital Repository @ Iowa State University,

Copyright Owner

Kevin Allen Cook



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99 pages