Genetics

Question 1

What is the premise of precision medicine?

Answer 1

It takes into account individual variability in genes, environment, and lifestyle for each person, so only the people who will benefit from the treatment will be given it.

Question 2

What is the amount of protein produced determined by?

Answer 2

1) Rate of transcription (manufacture of Pre-mRNA)
2) Rate of splicing to mRNA
3) Half life of mRNA
4) Rate of processing of polypeptide

Question 3

What are polymorphisms?

Answer 3

Any variation in the human genome that has a population frequency of greater than 1% or any variation in the human genome that does not cause a disease in its own right.

Question 4

What are acrocentric chromosomes?

Answer 4

Chromosomes that only have a long arm

Question 5

What does it mean to have a balanced chromosome rearrangement?

Answer 5

All the chromosomal material is present

Question 6

What is an unbalanced chromosome rearrangement?

Answer 6

There is extra or missing chromosomal material. Usually 1 or 3 copies of some of the genome.

Question 7

What is Aneuploidy?

Answer 7

Whole extra or missing chromosome.

Question 8

What is a translocation?

Answer 8

The rearrangement of chromosomes

Question 9

What are microdeletions?

Answer 9

Deletions too small to see at the chromosome level

Question 10

What is a Robertsonian Translocation?

Answer 10

When two acrocentric chromosomes become stuck end to end.

Question 11

Why is X chromosome aneuploidy better tolerated?

Answer 11

Because of x-inactivation

Question 12

What does unbalanced translocations result in?

Answer 12

Miscarriage (when large segments are translocated) or a dysmorphic delayed child (when small segments are translocated).

Question 13

What can molecular cytogenetics not detect?

Answer 13

Balanced chromosome rearrangements

Question 14

Why does somatic mosaic occur?

Answer 14

Because all cells suffer mutations as they divide.

Question 15

What can chromosome changes do that might cause cancer

Answer 15

Activate an oncogene or delete a tumour suppressor

Question 16

Explain seven types of mutation

Answer 16

• Promotor Mutation- results in no or reduced transcription and in some cases no protein.
• Splice Consensus altered- results in different transcription and abnormal protein as introns may remain in the mature transcript.
• Nonsene Mutation- change in base results in a stop codon being coded for so transcription is terminated early.
• Missense Mutation- change in one base results in a different amino acid being coded for.
• Insertion- base is added which results in a frame shift mutation.
• Deletion- one bases or sections of code are deleted.
• Expansion- part of a code is repeated

Question 17

What does it mean if an insertion or deletion is in frame?

Answer 17

The reading frame is not altered by the change i.e. the number of added or deleted nucleotides is divisible by three.

Question 18

What is penetrance?

Answer 18

The likelihood of having a disease if you have a gene mutation.

Question 19

Name and explain 3 types of mendelians inheritance

Answer 19

1. Autosomal dominant (Mendelian)- if you get one copy of the abnormal gene you will get the disease.
2. Autosomal recessive (Mendelian)- two copies of the abnormal gene must be present for the individual to get the disease.
3. X-linked (Mendelian)- mutation of the X chromosome causes the disease, males more likely to be affected as only one X chromosome so cannot mask any abnormalities.

Question 20

What is multifactorial inheritance?

Answer 20

Basically refers to everything that isn’t Mendelian inheritance, genetic contribution to any disease process.

Question 21

What are copy number variations?

Answer 21

Extra or missing sections of genetic material.

Question 22

Name four genes that are involved in cancer

Answer 22

Oncogenes
Tumour suppressors
DNA repair genes
Drug metabolism genes (that metabolise carcinogens)

Question 23

Explain the difference between driver and passenger mutations

Answer 23

Driver mutations: mutations that drive carcinogenesis

Passenger mutations: incidental mutations that happen because the tumour is unstable

Question 24

Explain DNA methylation is relation to cancer

Answer 24

• DNA Methylation is the addition of a methyl group that usually occurs on cytosine bases just before guanine bases. Methylation represses transcription of that gene, if that gene is a promotor then transcription will not happen.
• Methylation is an epigenetic modification, changes in the chemical structure but not the sequence.
• Methylation makes mutation (C to T) more likely
• Abnormalities of methylation cause genetic disease
• Methylation causes gene silencing in cancer

Question 25

Explain Knudson’s “Two Hit” Hypothesis

Answer 25

• You can inherit a cancer disposition or get the same cancer through acquired mutations. Often you need two copies of gene for tumour to develop.
• Both genes could be affected by somatic mutation though or one copy may be inherited.