Figure 2.—

Breeding of targeted mice and color change after removal of the neo-cassette. (A) Coat appearance of wild type, heterozygous, and homozygous S73A-neo mice and corresponding genomic Southern analyses. Both wild-type and heterozygous mice are normally pigmented while homozygotes are largely white except for pigmented spots seen in 15–20% of the animals as shown in the example. Genomic DNA was digested and probed as described in Figure 1 for ES cells. The targeted heterozygous mouse shows the expected Southern pattern (although with different intensities for the wild-type and recombinant bands, particularly clear with XbaI and the 5′ probe) and the homozygous mouse shows wild-type and recombinant bands of equal intensities. (B) Compound heterozygotes of the indicated genotypes are white mice. (C). After Cre-mediated recombination to remove the neo-cassette, homozygous mice (labeled S73A-Δneo/S73A-Δneo) are largely gray but have extensive white spotting and at least one darkly pigmented area. Also, they retain a wild-type PCR band as indicated at the bottom of the figure. The solid triangles represent the loxP site. For details, see text.