Genotyping of pre-implantation embryos. A nested PCR strategy was used to genotype embryos prior to implantation as described in Figure 4. Capn2+/- mice were mated and the date of fertilization established by the appearance of vaginal plugs. Blastocyst (E3.5) or 8-cell embryos (E2.5) were flushed from the oviducts and then digested with proteinase K. In separate reactions segments found exclusively in either the wild-type or mutant alleles were co-amplified with an internal control sequence, located in the short (upstream) arm of the targeting vector, which is found in both alleles. The final products were 429 bp for the wild-type allele, 389 bp for the mutant allele, and 213 bp for the internal control. (A) A representative example of the genotyping of blastocyst stage embryos. Embryos #1, 2, 4, 5, and 6 were Capn2+/- whereas embryos #3 and #7 were Capn2+/+, denoted by the absence of the 389 bp mutant signal. (B) An example of the genotyping of 8-cell embryos is shown. Embryos #1, 2, 3, 5, and 6 were Capn2+/- while embryo #4 was Capn2-/-, marked by the absence of the 429 bp wild-type signal. (M) denotes the molecular weight marker.