FIG. 1.

(A) Generation of a null allele of the SDHD gene. Gene targeting replaced the wild-type allele by a nonfunctional allele lacking exons 2, 3, and 4. The two homologous fragments of genomic DNA (4.0 and 4.4 kb) flanking the prokaryotic neomycin resistance (neo) gene allow for homologous recombination. B, BamHI; H, HindIII. (B) Selected ES cell clones were analyzed for correct gene targeting at the SDHD locus by Southern blotting. Digested DNA was hybridized with the indicated probes, giving additional bands of the indicated sizes in the heterozygous (+/−) ES clone with respect to the homozygous wild type (+/+). (C). Southern blot genotyping of SDHD knockout mice.