Lecture 2

Question 1

What are the mechanisms for recessive and dominant conditions and the implications for therapy?

Answer 1

dominant - caused by the production of a toxic protein and the treatment involved neutralising the protein

recessive - absence of a working gene and so the treatment involved the restoration or insertion of a functioning one

Question 2

What is penetrance?

Answer 2

frequency with which the symptoms are present

Question 3

What is variable expressivity?

Answer 3

the degree of severity in an individual

Question 4

What is phenocopy?

Answer 4

disease with the same phenotype ad the the genetic but doesn’t have genetic cause

Question 5

What is epistasis?

Answer 5

interaction between the disease causing genes mutations and the other modifiying genes affecting the phenotype

Question 6

What is genetic heterogeneity - the types and give examples?

Answer 6

Same gene, different mutations and so different disease - cystic fibrosis and CAVD

Same disease, different genes - Haemophilia A+B

Same disease, different genes and inheritance patterns - epidermolysis bullosa

Question 7

What is gene dosage compensation?

Answer 7

Organisms equalise the amount of gene expressed between members of different sexes so one X chromosome in females is randomly inactivated in each cell (X inactivation)

Question 8

How can an individual be genetically one sex but phenotypically another?

Answer 8

SRY recombination so XX individuals have testes but are infertile and XY individuals are also infertile

Question 9

Give an example of an autosomal dominant disease

Answer 9

Huntington’s disease
Motor, cognitive and psychiatric dysfunction
Hyperkinesia (muscle spasms)
No cure
Mutated HTT (chr 4)
Huntington protein forms clumps in organs and leads to cell death in the basal ganglia
Repeats in CAG which increase with each generation
Repeats 40-120 mean affected

Question 10

Give an example of an autosomal recessive condition

Answer 10

Cystic fibrosis
Severity varies between individuals
Mutated CFTR (chr 7)
This transporter normally pumps chloride ions into the mucus which draws water in and reduces its thickness. This doesn’t happen so thick mucus is made.
The mucus affects breathing and blocks the pancreas so enzymes cannot be secreted.
The most common mutation is delta F508 which affects the folding of the protein and its transportation to cell surface.

Question 11

Give an example of an X linked recessive condition

Answer 11

Haemophilia
Blood clotting disorder and results in easy bruising
Two types - A+B
A - caused by F8 mutation coding for clotting factor 8
B - caused by F9 mutation coding for clotting factor 9