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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Autosomal Dominant Inheritance. Only one "affected" allele is necessary to result in the "affected" phenotype. For a genetic disease inherited in this manner, only one mutant allele is necessary to result in the phenotype. Achondroplasia (discussed later) is an example of a dominant disorder. Both homozygous and heterozygous individuals will show the phenotype. Homozygous achondroplasia is usually a lethal condition. Answer: allele
Output:
In autosomal dominant inheritance only one "affected" what is necessary to result in an "affected" phenotype?