Our F1 and F2 genotyping also revealed that Chrd−/−,Tbx1+/G>T mice (in which one Chrd null allele was inherited from the129S6 strain and one from B6) had very few 22q11DS phenotypes (1/53 for F2 animals; Figure 2D). Here, TBX1 is linked to 22q11.2 deletion syndrome.