Insertion of a eGFP gene in-frame to sequences encoding the Hoxa1 gene. An adjacent loxP-flanked neomycin cassette was removed via Cre-mediated recombination in mice in this derivative of Hoxa1tm3Mrc. A Hoxa1-eGFP fusion protein is expressed from this allele in a pattern identical to that predicted by in situ hybridization analysis.