Biology Department Seminar

Evolutionary analysis of duplicated genes suggested that maize might have arisen by allotetraploidy, indicating the hybridization of two slightly diverged progenitors rather than the duplication of a single progenitor. Recent comparisons of orthologous chromosome intervals from these two chromosome sets with sorghum and rice showed that the two progenitors of maize and the progenitor of sorghum nearly split the same time, 11.9 million years ago (mya). The speciation of maize might have occurred as recently as 4.8 mya. New data sets have been used to extend these studies. From those, it appears that diploidization of maize was also accompanied by extensive losses of one copy of the duplicated (orthologous) genes and at the same time by the increase of paralogous gene copies either in tandem or scattered around the genome, indicating a remarkable mobility of genes or gene fragments. Comparison of haplotypes of alpha zein gene clusters shows that some loci are conserved in their degree of gene amplification and collinearity of genes, others are not. Interestingly, some paralogous non-zein genes appear to have arisen by helitron movement, illustrating one possible mechanism of the dispersal of genes and gene fragments throughout the genome. Furthermore, differential gene amplification can lead to a switch in differential transcriptional control, affecting the penetrance of certain phenotypes. Therefore, maize hybrids appear to be a major source for creating new haplotype combinations for target genes and their control factors. These combinations can be fixed through inbreeding, which is illustrated by the alignment of orthologous chromosomal regions.