Effects of Mutations II - Lecture 20

Question 1

What is haploinsufficiency?

Answer 1

A mutation is one gene will cause a disease due to reduction in amount of gene product

Question 2

What is MFDGA?

Answer 2

○ Craniofacial disorder caused by haploinsufficiency of RNA splicing factor EFTUD2
○ Defective RNA splicing of pre-mRNAs required for development
○ Neural crest cells don’t migrate properly

Question 3

What is the difference between sporadic and familial retinoblastoma?

Answer 3

○ Retinoblastoma = cancer of the retina
○ Sporadic = Two functional copies of a tumor suppressor gene becomes mutated and inactivated (rare)
○ Familial = only one functional copy of tumor suppressor gene so more likely to get retinoblastoma

Question 4

What diseases are caused by deletion mutations?

Answer 4

Deletion of about 500kb from the X chromosome can lead to immune disorders

Question 5

What diseases are caused by trisomy and monosomy?

Answer 5

○ Trisomy = Down syndrome caused by three copies of chromosome 21
○ Monosomy = bone marrow failure and high risk of leukemia as one copy of chromosome 7 is missing

Question 6

What is chromosome translocation?

Answer 6

○ When part of one chromosome becomes attached to another chromosome
○ Some types of translocation are relatively common
○ Example: exchange of segments between chromosomes 9 and 22 (change chromosome 22 known as Philadelphia chromosome)

Question 7

What is the Philadelphia chromosome a common cause for?

Answer 7

○ Leukemia
In a normal abI gene:
- Second messengers controlled by external signals interact with this part of the DNA
- they switch on the abI gene when the abI protein is needed
- Cell division is stimulated in response to signal from outside the cell
In a mutated abI gene:
- Gene is switched on all the time so cell division is uncontrolled
- Control region has been lost

Question 8

What are examples of advantageous mutations?

Answer 8

○ R173C missense mutation = low prevalence of cardiovascular disease in carriers
○ G171V missense mutation = high bone density and less broken bones in carriers of this mutation
○ Loss of MC1R function (red hair) = increased pain sensitivity
○ DEC2 missense mutation = natural short sleep