**1. Introduction**

196 Gene Duplication

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Eukaryotic gene expression is often controlled by complex and refined combinatorial transcription factor networks composed of multiprotein complexes that derive their gene regulatory capacity from both intrinsic properties and from their *trans*-acting partners (Singh, 1998; Wolberger, 1998; Remenyi *et al.*, 2004). Participation in such higher complex order allows an organism to use single transcription factors to control multiple genes with different temporal and spatial expression patterns (Siefers *et al.*, 2009).

In this chapter, we provide a synopsis of the genetic and genomic mechanisms that might be responsible for the gene copy diversification observed in the eukaryotic NF-Y transcription factor family. We identify the genes coding for NF-Y transcription factors in eukaryotes with an emphasis on the duplication of the NF-Y family in the plant lineage and discuss the important consequences of its gene diversification.
