<i>malf</i> homozygotes have craniofacial defects that include primarily misplaced ears and, in some instances, significant asymmetry of the snout. The ear pinnae can be smaller than normal, misshapen, and positioned lower than normal and this can affect one or both ears. The phenotype ranges from subtle to pronounced. Of 37 mutants 28 had the left pinna affected, 8 had the right pinna affected and 1 had both affected. The parental phenotype does not appear to instruct which ear is affected. Of 117 offspring from homozygous x heterozygous or heterozygous x homozygous crosses only 39 (33%) were clearly mutant, indicative of either incomplete penetrance or partial embryonic lethality. In a mapping cross to C3H/HeSnJ only nine mutants were identified in one hundred seven F2 hybrids (8.4%). No mutants were identified in twenty-eight F2 hybrids with FVB/NJ, thirty-four F2 hybrids with CAST/EiJ, or nine F2 hybrids with A/J. 

This spontaneous mutation provides a model for craniofacial developmental defects including low set ears and twisted snout.

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