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Figure 1. Schematic representation of the pattern of the lower cheek tooth primordia in wild-type (WT) and tabby (Ta) mouse fetuses (according to Peterkova et al., 2002). M1, M2, and M3—the first, second, and third lower molar primordia in WT mice. T1, T2, and T3—the prospective first, second, and third functional teeth in the different subtypes of Ta morphotypes I (Ia, Ib, Ic) and II (IIa, IIb). Note the decreasing volume of the most mesial tooth primordium from subtypes Ia to IIb, which is associated with increasing volume of the subsequent tooth primordia and a mesial shift in tooth boundaries compared with WT mice. The abortive tooth primordium (dashed line) represents an abortive cap (**) in subtype IIa and an abortive bud (*) in subtype IIb. These abortive tooth primordia do not give rise to a functional tooth. The first functional tooth (T1) in morphotype II is, in reality, the second tooth primordium, which originates in the mesio-distal sequence during odontogenesis. Accordingly, the morphology of T1 in morphotype II is similar to that of T2 in morphotype I (Peterkova et al., 2002).
