Mouse artificial chromosome (MAC) technology cloned the 34 MB long arm of HSA21 (HSA21q). The MAC transgene contains a CAG promoter driving the EGFP reporter gene flanked by HS4 insulators, a PGK-neomycin cassette, loxP-3'HPRT site, PGK-puromycin cassette, and telomeres. Line 1 was generated.