Fig. 1. Cre-mediated recombination of the Tbx1^flox allele and effects of TM on embryonic viability. (A) Schematic of the polymerase chain reaction (PCR) strategy used to evaluate Tbx1^flox recombination. The primer pair (arrows) amplifies fragments of different lengths from the Tbx1^flox and wild-type alleles of Tbx1^flox/+ cells but not from the Tbx1^E5 allele (which results from Cre-mediated recombination of Tbx1^flox). (B) Representative PCR results from genomic DNA extracted from individual Tbx1^flox/+ embryos (controls, Cre-) and TgCAGG-CreER^TM;Tbx1^flox/+ embryos exposed to TM in utero for the time indicated. There is progressive fading of the Tbx1^flox amplicon. (C) The plot indicates the progressive decrease in the intensity (percentage) of the Tbx1^flox amplicon compared with the Tbx1⁺ amplicon. Each point is the average of measurements from 12-17 embryos. Error bars indicate standard deviation. (D) Numbers of dead embryos at various harvest stages after TM injection at the time points indicated.