The Addams family has an autosomal dominant condition in which webbing attaches the second toe to the third toe and the second toe is longer than the big toe. Only some of the Addams' who inherit the mutant allele have a second toe longer than the big toe. In addition, the extent of webbing varies. This phenotype is:. a. both inherited and non-inherited. b. dominant and recessive. c. invariably expressive and completely penetrant. d. variably expressive and incompletely penetrant.