Records for ALDH genes were retrieved and sorted for all 11 species analysed (Table 1). The number of records that met the above-mentioned criteria is provided (ie the number of genes excluding nonfunctional pseudogenes). The number of ALDH genes per species varied from 14 in chicken to 25 in zebrafish. There are currently 207 distinct genes present within the database for these 11 species; this is a greater than fourfold increase from 2002, when only 51 were annotated [10]. This allows for a much more comprehensive comparison of ALDH superfamily members throughout vertebrate evolution during the past 450 million years. It is important to keep in mind that, for many species, some genes have yet to be identified. Further, many annotated genes may reflect gene-duplication events that represent non-functional pseudogenes. These situations will be explored in greater depth below.
