Phenotype Variability in Genetic Disorders

During investigations of a rare genetic disorder, researchers discovered a novel phenotype associated with a mutation in a gene coding for a signal transduction protein. The mutation results in the protein being unable to bind its ligand effectively, leading to a loss of downstream signaling in the affected pathways. The phenotype observed includes abnormal cell growth and differentiation in tissues, reminiscent of the overactivation seen in oncogenic signaling.

Given that this genetic disorder shows an autosomal dominant inheritance pattern, the researchers conducted a study involving a cohort of affected individuals. They found varying penetrance of the phenotype, with some individuals carrying the mutation displaying no observable symptoms, while others exhibited severe manifestations. Additionally, family studies revealed that offspring of affected individuals had a 50% chance of inheriting the mutant allele.

Based on this information, which of the following best explains the observed variability in phenotype among individuals with the same genetic mutation?