Both genetic and nongenetic factors cause the congenital skeletal abnormality known as clubfoot, which occurs with a worldwide incidence of about 1 in 1000 births. gurnett et al. identified a family in which clubfoot occurred as an autosomal dominant trait due to a mutation in the pitxi gene. dna testing revealed that 11 people in the family carried the pitxi mutation, but only 8 of these people had clubfoot. calculate the penetrance of the pitxi mutation in this family.