Targeting constructs used to create mutant Hfealleles. The structures of the two targeting constructs are shown, with reference to the murine Hfe locus. In each case, the intron/exon structure of the genomic clone is shown on the top line, the structure of the targeting construct is shown on the second line, and the structure of the correctly targeted mutant locus is shown on the third line. Black boxes are Hfe exons. Translational start (ATG) and stop (STOP) sites are indicated. 5′ homology (5′ hom) and 3′ homology (3′ hom) regions are indicated for each targeting vector. The locations of the neomycin resistance (NEO) and cytosine deaminase (CD) cassettes are shown. Hatched boxes represent loxP sites. The asterisk (*) shows the site of codon 282. (a) Summarizes the strategy used to make the null allele; (b) summarizes the strategy used to introduce the C282Y missense mutation. The final line in (b) shows the structure of the C282Y allele after vector sequences have been removed by Cre-mediated recombination between loxP sites.