Microarray analysis of gene expression patterns in immature ear, seedling, and embryo tissues from the
maize inbred lines B73 and Mo17 identified numerous genes with variable expression. Some genes had
detectable expression in only one of the two inbreds; most of these genes were detected in the genomic
DNA of both inbreds, indicating that the expression differences are likely caused by differential regulation
rather than by differences in gene content. Gene expression was also monitored in the reciprocal F1
hybrids B73 3 Mo17 and Mo17 3 B73. The reciprocal F1 hybrid lines did not display parental effects on
gene expression levels. Approximately 80% of the differentially expressed genes displayed additive expression
patterns in the hybrids relative to the inbred parents. The 20% of genes that display nonadditive
expression patterns tend to be expressed at levels within the parental range, with minimal evidence
for novel expression levels greater than the high parent or less than the low parent. Analysis of allelespecific
expression patterns in the hybrid suggested that intraspecific variation in gene expression levels is
largely attributable to cis-regulatory variation in maize. Collectively, our data suggest that allelic cisregulatory
variation between B73 and Mo17 dictates maintenance of inbred allelic expression levels in the
F1 hybrid, resulting in additive expression patterns.