5.4 Phenotypic Variability

Question 1

What is meant by phenotypic variability?

Answer 1

Variation of gene expression in the same disease in different individuals, such that individuals with the same genetic disease may not have the same symptoms or presentations

Question 2

What are the 5 reasons as to why phenotypic variablity exists? MUMES

Answer 2

Mutations
Unstable
Modifiers
Environment
Sex

Question 3

What is meant by modifiers?

Answer 3

When the expression of one gene directly affects the presence of other genes

Question 4

How do different mutations within the same gene affect the phenotype of a disease?

Answer 4

Different subtypes of the same disease have different presentations

Question 5

What is an example of how sex affects the phenotype of a disease?

Answer 5

In hereditary haemochromatosis – women lose blood through mensturation and therefore generally have lower iron levels

Question 6

How do different mutation in the same gene lead to different phenotypes?

Answer 6

Duchenne vs Becker muscular dystrophy – slightly different mutations of the same dystrophin gene cause different presentations

Question 7

What is an example of how modifiers affect the phenotype of a disease?

Answer 7

In cystic fibrosis, the number of gene variations interacting with CF mutation changes the phenotype

Question 8

What are trinucleotide repeat disorders?

Answer 8

Where an increased number of nucleotide repeats (>27) cause more severe phenotypes throughout generations

Question 9

What affect do trinucleotide repeats have on the proteins produced?

Answer 9

Changes protein function

Question 10

What does a larger number of trinucleotide repeats result in?

Answer 10

More severe phenotype and earlier onset of disease

Question 11

If you have less than how many TNR’s is the mutation considered stable?

Answer 11

Less than 27

Question 12

If individuals are identical, and there is variation in the phenotype, what is likely to have caused the variation?

Answer 12

The environment

Question 13

In non-identical individuals with the same mutation, what could cause the variation in phenotype?

Answer 13

The presence of other genes as well as the environment

Question 14

In unrelated individuals, how does phenotypic variability arise?

Answer 14

Due to unstable mutations like TNRs

Question 15

If there is a binary presentation of a condition eg half a family have a condition and half don’t, what is likely to cause the variation?

Answer 15

The presence of a second gene modifying the disease phenotype

Question 16

If there are two forms of the same disease, and one is a milder phenotype, what is likely to cause the variation?

Answer 16

Mutations - Different mutations of the same gene results in different diseases

Question 17

When there is wide variation in a condition but the variation does not apply to monozygotic twins, what is likely to be causing the variation?

Answer 17

A second gene which the twins did not inherit

Question 18

When there is marked variability and no two members being affected in the same way, what is likely to cause the variation?

Answer 18

Environment

Question 19

When there is a large difference in the age of onset between family members, what is likely to cause this variation?

Answer 19

Unstable mutations

Question 20

What cause of variation is more likely to have transgenerational effects?

Answer 20

The expansion of unstable trinucleotide repeats