ALDH1A1 is present in all species except zebrafish, confirming earlier studies [23]. In cow, there are two distinct records for ALDH1A3: the gene found on Chr 21 is full length (537 AAs) and represents the putatively functional parent gene (ALDH1A3), whereas the second is a detritus pseudogene on Chr 28 which appears to the product of a partial gene-duplication event (ALDH1A3P1). The shorter genomic sequence would translate a peptide sharing 100 per cent sequence identity to only the 127 carboxy-terminal AAs of the full-length parent protein. Several gene duplications appear to have been conserved in rodents. One such gene is ALDH1A7, found in rats and mice. In both cases, the ALDH1A7 gene is present on the same chromosome and in close proximity to ALDH1A1. Mouse ALDH1A7 shares 92 per cent AA identity with mouse ALDH1A1, and studies have confirmed that the gene encodes inducible tissue-specific mRNA [24]. ALDH1B1 is present in mammals but missing from birds and fish. ALDH1L1 is missing from both bird species (zebra finch and chicken) but present in other species examined and thus may represent a deletion in the avian lineage.
