Penetrance And Expressivity

Question 1

What is expressivity ?

Answer 1

Expressivity refers to the extent to which a particular genotype is expressed in the phenotype of an individual. (The severity of phenotype)

Eg Marfan’s disease has a very varied expressivity, meaning different people affected by it can be affected very differently.

Question 2

What is anticipation ?

Answer 2

Age of onset of a condition gradually decreases with each successive generation

Eg - HUNTINGTON DISEASE
MYOTONIC dystrophy
Fragile- X - syndrome

Question 3

What is methylation ?

Answer 3

process by which genes can be silenced (i.e. not transcribed) by the addition of methyl groups.

Question 4

What is penetrance?

Answer 4

refers to the proportion of the population who have a particular mutation also having the associated disease.

An example would be BRCA-1, a mutation of which causes breast cancer in 80% of those affected, giving it a penetrance of 80%.

examples of conditions with incomplete penetrance include retinoblastoma and Huntington’s disease

in contrast, achondroplasia shows 100%, or complete, penetrance