Genetic Basis of Disease

Question 1

In terms of the genetic basis of disease, what is meant when a particular mutated gene is
referred to as being autosomal recessive?

Answer 1

This refers to the fact that the gene does not occur on a sex chromosome (occurs on any
other chromosome) and that it requires both alleles to have that genotype (homozygous)
in order to see the disease phenotype

Question 2

What are some of the numerical or structural chromosomal abnormalities that can occur?
Provide a brief description of each.

Answer 2

Aneuploidy: an increase or decrease in number of chromosomes
Deletion: part of a chromosome is lost
Duplication: part of the chromosome is duplicated
Inversion: chromosome breaks and reattaches in the opposite orientation
Translocation: movement of a piece of chromosome from one region to another
Ring: two ends of a chromosome join

Question 3

Provide an example covered in lectures of a disease caused by a chromosomal
translocation.

Answer 3

Chronic myelogenous leukaemia (CML).

Question 4

What is meant by the term “epigenetics”?

Answer 4

This is the study of heritable changes to the genome that do not alter the sequence of the
DNA but rather affect the expression of genes.

Question 5

Name an epigenetic chemical modification that occurs to DNA and where this occurs.

Answer 5

Methylation of cytosines

Question 6

Which two processes regulating cell proliferation allow for cancer development when
they are perturbed?

Answer 6

Mitosis and apoptosis

Question 7

List three hallmarks of cancer.

Answer 7

-sustained proliferative signalling
-evading growth suppressors
-avoiding immune destruction

Question 8

What is a tumour suppressor gene?

Answer 8

A tumour suppressor gene encodes a protein with an anti-proliferative/pro-apoptotic
role that prevents cancer development

Question 9

Give two examples of tumour suppressor genes

Answer 9

p53, PTEN

Question 10

What is a proto-oncogene?

Answer 10

These are genes that usually help cells grow and avoid cell death. But when they have changes or mutations, they can encourage excessive cell growth, which can lead to cancer.

Question 11

Give two examples of oncogenes.

Answer 11

Ras, B-Raf

Question 12

What is the RISC?

Answer 12

RISC = RNA-induced silencing complex. This is a large (~500 kDa) RNA-
multiprotein complex, which triggers mRNA degradation in response to siRNA.

Question 13

What is the catalytic component of RISC?

Answer 13

The Argonaute protein

Question 14

What are antisense oligonucleotides?

Answer 14

Antisense oligonucleotides (ASOs) are single-stranded nucleic acids that target
specific RNA sequences by complementary base-pairing.

Question 15

What does the term “splice-switching oligonucleotide” mean and what is the mechanism
of action of splice-switching oligonucleotides?

Answer 15

SSOs modulate splicing by binding to the RNA and sterically
blocking splicing factors or splice sites

Question 16

What is CAR-T cell therapy?

Answer 16

A type of cancer immunotherapy treatment that uses immune cells (T cells) that are
genetically engineered to enable them to identify and destroy cancer cells more effectively

Question 17

What is the difference between in vivo and ex vivo gene therapy?

Answer 17

In vivo gene therapy involves direct injection of the gene into the target cells, whereas ex
vivo gene therapy involves the removal of cells from an individual, growing the cells
outside of the body in culture, introducing the genes into the cultured cells and reinjection
of the cultured cells back into the body

Question 18

How have CAR-T cells been modified to make them effective in identifying and
destroying cancer cells?

Answer 18

CAR-T cells are special immune cells that have been modified in a lab. They’re given a special receptor called a “CAR” that helps them do two important things at once to fight diseases.
The CAR recognizes the tumour via a specific interaction of the receptor portion of the CAR with surface proteins on the cancer cells .

Question 19

What is the function of the enzyme Dicer?

Answer 19

Dicer is a member of the RNase III family of nucleases that specifically cleave
double-stranded RNAs. Dicer processes long dsRNA into siRNA of 20-24 nt.

Question 20

What is the function of Drosha?

Answer 20

Drosha is an RNase III family member that processes pri-MRNA to become 70nt
hairpins called pre-miRNA.

Question 21

What are the differences between siRNAs and miRNAs?

Answer 21

miRNA: microRNA.
Encoded by endogenous genes.
Hairpin precursors - pre-miRNAs
Recognize multiple targets.

siRNA: short-interfering RNA.
Mostly exogenous origin.
Target specific
dsRNA precursors

Question 22

Antisense oligonucleotides can have different possible effects following their
interaction with RNA. What are these possible effects and what is the consequence on
gene expression?

Answer 22

Binding of an ASO to its complementary RNA sequence can result in mRNA cleavage
(1/2) or inhibition of translation (1/2), both of which would lead to less protein
production (1). Alternatively, ASO binding can result in splicing modulation (1) that
leads to expression of splice variants or alternative isoforms of a gene (1).