penetrance_expressivity_flashcards
What do penetrance and expressivity describe?
The degree to which patients with the same gene mutation exhibit observable characteristics.
What is penetrance?
The proportion of a population of individuals who carry a disease-causing allele who express the related disease phenotype.
What is expressivity?
The extent to which a genotype shows its phenotypic expression in an individual.
What factors are thought to influence penetrance and expressivity?
Modifier genes, environmental factors, allelic variation.
How is penetrance described?
‘How likely’ it is that a condition will develop.
Give examples of conditions with incomplete penetrance.
Retinoblastoma and Huntington’s disease.
Give an example of a condition with complete penetrance.
Achondroplasia.
How is expressivity described?
The ‘severity’ of the phenotype.
Give an example of a condition with a high level of expressivity.
Neurofibromatosis.
