title: Measuring gene expression divergence: the distance to keep.
abstract: BACKGROUND
  Gene expression divergence is a phenotypic trait reflecting evolution of gene regulation and characterizing dissimilarity between species and between cells and tissues within the same species. Several distance measures, such as Euclidean and correlation-based distances have been proposed for measuring expression divergence.
  
  
  RESULTS
  We show that different distance measures identify different trends in gene expression patterns. When comparing orthologous genes in eight rat and human tissues, the Euclidean distance identified genes uniformly expressed in all tissues near the expression background as genes with the most conserved expression pattern. In contrast, correlation-based distance and generalized-average distance identified genes with concerted changes among homologous tissues as those most conserved. On the other hand, correlation-based distance, Euclidean distance and generalized-average distance highlight quite well the relatively high similarity of gene expression patterns in homologous tissues between species, compared to non-homologous tissues within species.
  
  
  CONCLUSIONS
  Different trends exist in the high-dimensional numeric data, and to highlight a particular trend an appropriate distance measure needs to be chosen. The choice of the distance measure for measuring expression divergence can be dictated by the expression patterns that are of interest in a particular study.
authors.affiliation: Department of Biostatistics and Computational Biology, University of Rochester Medical Center, Rochester, NY 14642, USA. galina_glazko@urmc.rochester.edu
authors.forename: Galina
authors.initials: G
authors.lastname: Glazko
authors.forename: Arcady
authors.initials: A
authors.lastname: Mushegian
mesh_terms: D000818:Animals; D019143:Evolution, Molecular; D015870:Gene Expression / Q000235:genetics*; D006801:Humans; D010802:Phylogeny; D051381:Rats