The transgene comprises a yeast artificial chromosome (YAC) from the CEPH Whole Genome MegaYAC Library carrying a 670-kb fragment of DNA from human Chromosome 21 containing the genes CBR1 (carbonyl reductase 1), CBR3 (carbonyl reductase 3), DOPEY2 (dopey family member 2; formerly C21orf5), MORC3 (MORC family CW-type zinc finger 3; formerly KIAA0136), and CHAF1B (chromatin assembly factor 1, subunit B (p60)). This transgenic line was shown by Southern blot analysis to bear a single copy of the YAC. (J:128897)