The genetical difference between the DBA/2 and C57Bl/6 strains in cortisone-induced cleft palate

The DBA/2 strain of mice is about five times more sensitive than the C57B1/6 strain to cortisone-induced cleft palate. There is a matroclinous reciprocal cross difference. Appropriate backcrosses indicate that the basis of this reciprocal cross difference is not cytoplasmic. A biometric model including additive and dominance components adequately explains the data. Since dominance has been demonstrated in other strains and crosses, it is suggested that a trait correlated to cortisone-induced cleft palate has been exposed to directional selection.