Phenotypic Variability

Question 1

how many types of OI are there?

Answer 1

9 types

Question 2

what are muscular dystrophies?

Answer 2

group of diseases which cause progressive weakness and muscle breakdown

Question 3

what are the 2 most common types of muscular dystrophy?

Answer 3

duchenne muscular dystrophy
becker muscular dystrophy

Question 4

What is meant by phenotypic variability?

Answer 4

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 5

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

Answer 5

Mutations
Unstable
Modifiers
Environment
Sex

Question 6

What is meant by modifiers?

Answer 6

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

Question 7

What is meant by the effects of mutations on the phenotype of a disease?

Answer 7

Different subtypes of the same disease have different presentations, due to mutations within the same gene

Question 8

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

Answer 8

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

Question 9

What is an example of how different mutations in the same gene affect the phenotype of a disease?

Answer 9

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

Question 10

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

Answer 10

In CF, the variety of genes present can increase the degree of

also eye colour

Question 11

What are trinucleotide repeat disorders?

Answer 11

when a region of three repeated nucleotides in the genome increases in number during DNA replication (>27) cause more severe phenotypes throughout generations

Question 12

What affect do trinucleotide repeats have on the proteins produced?

Answer 12

Changes protein function

Question 13

What does a larger number of trinucleotide repeats result in?

Answer 13

More severe phenotype and earlier onset of disease

Question 14

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

Answer 14

Less than 27

Question 15

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

Answer 15

The environment

Question 16

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

Answer 16

The presence of other genes (modifiers) as well as the environment

Question 17

In unrelated individuals, how does phenotypic variability arise?

Answer 17

Due to unstable mutations like TNRs, modifiers, environment, sex and others

Question 18

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 18

The presence of a second gene modifying the disease phenotype

Question 19

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

Answer 19

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

Question 20

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 20

A second gene which the twins did not inherit

Question 21

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

Answer 21

Environment

Question 22

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

Answer 22

Unstable mutations

Question 23

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

Answer 23

The expansion of unstable trinucleotide repeats