Figure 3.

Respiratory frequency of Hoxa2^-/- and Krox20^-/- mutants during the first postnatal days. Graphs present the evolution of mean ± standard error of the mean respiratory frequency in wild-type mice (open squares, dotted line) and (a) Hoxa2^-/- and (b) Krox20^-/- mutants (black triangles, continuous line) during the first two days after birth. All mutants were dead shortly after P0.75, therefore explaining the lack of further data. Deficiency of the respiratory frequency is lethal in Krox20^-/- [17]; frequency is normal in Hoxa2^-/- mutants. **P < 0.01, ***P < 0.001.