found that a high frequency of genes found on Chr 21 are duplicated on Chr 5 and none were identified on Chr 15, suggesting that Chr 5, rather than Chr 15, is the paralogous chromosome [28,29]. A similar situation was identified with respect to aldh9a1.2 on Chr 2. Uridine-cytidine kinase-2 homologues (uck2a and uck2b) are found upstream of both aldh9a1.1 and aldh9a1.2, supporting a tandem gene-duplication event; however, other genes in close proximity to this duplication do not show any homology between chromosomes 2 and 8.
