Lecture 18

Question 1

What is a polygenic trait?

Answer 1

An inherited trait that is controlled by multiple genes. These do not follow obvious inheritance patterns but are common in families and categorised in terms of risk. Environment may influence

Question 2

What are the two forms of polygenic traits?

Answer 2

Continuous and dichotomous traits

Question 3

What is a continuous complex trait?

Answer 3

Traits measured as a range e.g. height

Question 4

What is a dichotomous trait?

Answer 4

Traits measured at yes or no of having it

Question 5

What can contribute to polygenic traits?

Answer 5

Both environment and genes

Question 6

What is more rare, monogenic or polygenic traits?

Answer 6

Monogenic ~6% total worldwide affected

Question 7

Can people be affected by only one or more polygenic variants?

Answer 7

Can be affected by more than one at once

Question 8

What is the leading causes of death in the western world?

Answer 8

Polygenic variants

Question 9

What are examples of polygenic variants?

Answer 9

Type-2 diabetes, hypertension, heart disease, cancer, arthritis, mental health

Question 10

What are the two key concepts of polygenic traits?

Answer 10

Any type of protein can have a genetic variant and subsequently, a change in function; and proteins anywhere in a pathway/process can be affected

Question 11

What is the most serious loss of protein function in a pathway?

Answer 11

The first enzyme

Question 12

What does the loss of the first enzyme in a pathway result in?

Answer 12

Failure of the entire pathway to take place. This first chemical can build up which can be toxic

Question 13

What is an example of the loss of an enzyme at the start of a pathway?

Answer 13

Phenylketonuria

Question 14

What does the loss of an enzyme in the middle of a pathway result in?

Answer 14

Build up of chemicals in the middle

Question 15

What is an example of the loss of an enzyme in the middle of a pathway?

Answer 15

Human purine metabolism - hyperuricaemia

Question 16

What is an example of the loss of an enzyme at the end of a pathway?

Answer 16

ALDH2 deficiency

Question 17

What are the pros of polygenic genetic studies?

Answer 17

Polygenic traits are usually common therefore you can find a lot of people with the condition of interest and can design studies to account for environmental factors

Question 18

What are the cons of polygenic genetic studies?

Answer 18

Not looking for one gene/variant and a range of phenotypes are possible

Question 19

What is GWAS?

Answer 19

Genome-wide association studies

Question 20

What does GWAS do?

Answer 20

Studying people who already display the phenotypic disease and perform an association analysis for every marker

Question 21

How do cells grow normally?

Answer 21

Grow and divide to form new body cells as the body needs them (to heal injuries, grown bigger, to replace old cells)

Question 22

How is cancer characterised?

Answer 22

By the uncontrolled growth of cells, forming a tumour. The cells no longer respond appropriately to signals that control cell growth and death, leading to uncontrolled growth

Question 23

What happens to cancer cells over time?

Answer 23

They become increasingly resistant to growth control signals, dividing more rapidly

Question 24

What is a genetic variant?

Answer 24

A specific difference in DNA sequence between individuals

Question 25

What is a mutation?

Answer 25

The process by which new genetic variants arise (somatic)

Question 26

What are somatic cells?

Answer 26

All the different types of body cells

Question 27

What are germline cells?

Answer 27

reproductive cells involved in passing genetic information to the next generation

Question 28

What types of mutations can cause cancer?

Answer 28

Errors in DNA replication or exposure to a carcinogenic chemical causing damage to the DNA

Question 29

Why does the risk of cancer increase with age?

Answer 29

Cells are undergoing more division, there is more chance of error occuring

Question 30

What is the normal function of the immune system in relation to cancer cells?

Answer 30

It generally works to remove the cells before they cause problems

Question 31

What are the two cancer causing genes?

Answer 31

Proto-oncogenes and tumour suppressor genes

Question 32

What are proto-oncogenes called once they become mutated?

Answer 32

Oncogenes

Question 33

What are the proto-oncogenes?

Answer 33

Genes that encode proteins that promote cell growth

Question 34

What does a mutation in a proto-oncogene cause?

Answer 34

A dominant, gain of function mutation where cell grow is promoted when it is not required

Question 35

What are the tumour suppressor genes?

Answer 35

Genes encoding proteins that prevent uncontrolled cell growth

Question 36

What does a mutation in a tumour suppressor gene cause?

Answer 36

A recessive, loss of function mutation where cell growth is promoted instead of suppressed in order to control it

Question 37

What combination of mutations do you need for cancer to develop?

Answer 37

1x Oncogene and 2x tumour suppressor genes

Question 38

Why do you need all three?

Answer 38

If there is a mutation on only one then the other gene can compensate for that loss/gain of function

Question 39

Is cancer hereditary?

Answer 39

No, cancer cannot be passed on

Question 40

How does cancer tend to run in families?

Answer 40

The inheritance of mutated oncogenes/tumour suppressor genes is possible so they do not need to accumulate as many mutations in order to develop cancers

Question 41

What is the general trend in hereditary cancers?

Answer 41

They often develop at a much younger age