 Because of its focus on structure and the resulting usefulness for annotation practices in bioinformatics, the nominal gene remains the unit of analysis in comparative genomics (see  §1.5).  In these contexts, claims about similarity in terms of nominal molecular genes are often translated into claims of similarity more broadly construed, based on the assumption that homologous genes yield homologous products and hence are involved in homologous functions. Such claims are, however, often not warranted given the complexity of gene expression (Piotrowska 2009). On the other hand, much of genomic research seems not to be committed to any specific gene concept. Statistical techniques of bioinformatic sequence comparison function as discovery tools that detect relations between genome sequences, transcripts, and proteins or between sequences on any level among various species (Perini 2011). They can suggest candidate genes, indicate events of post-transcriptional processing, or point to processes of genome evolution (see  §§1.4–1.5).  Researchers in genomics (involving sequence annotation tasks), seem to respond to the complexities of regulation and post-transcriptional processing by operating with an extended structural characterization (“syntax-based”, in the parlance of bioinformatics-driven research) of genes and other genome elements, rather than emphasizing the ad hoc identification of genes from the perspective of products captured by the post-genomic gene concept (Baetu 2011, 2012a). A sequence thus characterized can still give rise to a variety of products, but their processing depends on splicing signals and similar sequence features that can be identified on a structural level. In this view, genes appear “as modular sets of instructions for the genome expression machinery of the cell” (Baetu 2011: 718).