Penetrance and expressivity

Question 1

Not all patients with the same gene mutation (i.e. genotype) exhibit the same degree of observable characteristics (i.e. phenotype). TRUE/FALSE

Answer 1

TRUE

Question 2

The proportion of a population of individuals who carry a disease-causing allele who express the related disease phenotype.

i.e. describes ‘how likely’ it is that a condition will develop

Answer 2

Penetrance

Question 3

The extent to which a genotype shows its phenotypic expression in an individual.

i.e. describes the ‘severity’ of the phenotype

Answer 3

Expressivity

Question 4

What factors can affect penetrance and expressivity

Answer 4

Modifier genes
Environmental factors
Allelic variation

Question 5

Give examples of conditions with incomplete penetrance

Answer 5

retinoblastoma and Huntington’s disease

Question 6

Give an example of a condition which has 100% or complete penetrance

Answer 6

achondroplasia

Question 7

give an example of a condition with a high level of expressivity

Answer 7

neurofibromatosis