Fig. 2. Overview of wild-type and mutant MTF-1 alleles. The gene structure of the wild-type MTF-1 allele is shown on top; below, two examples of spontaneous deletions that had occurred upon integration of the targeting DNA by homologous recombination are depicted. These deletions are missing 1.1 kb including exon 2 (allele MTF-1^61-2 and MTF-1^61-2R), or 4.1 kb including a substantial fraction of exon 1, together with the entire first intron and exon 2 (allele MTF-1^140-1 and MTF-1^140-1R). The targeting mutation in the initiator codon ATG→TTA in the original targeting construct is shown at the bottom (alleles MTF-1^140-1, MTF-1^61-2 and MTF-1^53-1R). Alleles MTF-1^61-2 and MTF-1^140-1 are duplications of the locus (as indicated in Figure 1) containing a ATG→TTA mutation in one copy and a deletion in the other copy of MTF-1. MTF-1^140-1R, MTF-1^61-2R and MTF-1^53-1R are alleles reduced to a single copy.