Incomplete penetrance causes traits to
Incomplete penetrance occurs when individuals possessing mutant genotype fail to develop phenotype due to suppressor alleles, environmental antagonism, age incompleteness, or stochastic threshold not reached. Consequently pedigree may show unaffecteds transmitting allele to affected descendants, creating apparent skipping of generations frequently misinterpreted as recessive or non-genetic. When modifier background or environmental trigger permits expression in later generation, trait reappears. This discontinuous pattern complicates Mendelian pedigree interpretation, risk prediction, and link
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 5: Pedigree Gaps from Incomplete Penetrance
