**9. Conclusion**

52 Gene Duplication

Fig. 3. Gene properties that can be examined for evidence of functional specialization. The top set (orange) are approaches that check for differences in gene regulation; expression levels reflect measurements of transcription in tissues in response to a series of stresses (e.g. as obtained from microarrays). The bottom set (blue) are aspects of the gene product that may differ between duplicates. Sequence logos may be generated using the WebLogo

software (Crooks et al., 2004).

Studies of the evolution of duplicate genes are pushing the field towards more exacting standards and definitions for gene function. Since the rate and extent of duplicate gene specialization is dependent on so many factors, and since novel functions can emerge in so many different ways, integrative approaches will be of paramount importance to understanding this key aspect of genomic evolution. Future studies can benefit in particular from the inclusion of data from gene families as a whole, as this additional information helps both with estimating ancestral gene functions and with evaluating the breadth of function previously covered by related genes.

While empirical evidence of differential catalytic function remains the gold standard for proving functional specialization of duplicated genes, high-throughput studies exploiting the vast quantities of minable expression data provide a cheap and effective means for studying functional specialization at the level of whole gene families. Genomes with annotations beyond expression profiles (such as gene-by-gene interaction profiles and essentiality data) should be helpful for determining the extent to which functional changes at the regulatory level actually impact phenotype.
