Genetics 3

Question 1

Describe the contribution of genetic and environmental factors

Answer 1

Some diseases are almost exclusively genetic (eg, cystic fibrosis) some diseases are a combination of both genetic and environmental (eg, heart disease) and some are almost exclusively environmental (eg, trauma) but still has some genetic factors

Question 2

What is quantitative inheritance?

Answer 2

Complex disorders and continuous traits which are influenced by multiple genes and multiple environmental factors

Question 3

What are single gene disorders?

Answer 3

Deterministic

Question 4

What are complex traits?

Answer 4

Even if you have all susceptibility alleles, disease still depends on environmental hazards.

Question 5

What is the liability threshold model?

Answer 5

Where all the factors which influence the development of a multifactorial trait/disorder can be considered as a single entity

Question 6

What is to the right of the threshold on a liability curve?

Answer 6

The incidence of disease in the general population

Question 7

What is the familial incidence?

Answer 7

The proportion above the threshold on a liability curve

Question 8

What is heritability of a trait/disease?

Answer 8

It is the proportion of the total variance that is genetic

Question 9

What is the overall variance of a phenotype?

Answer 9

The sum of the environmental and genetic variance.

Question 10

What is polymorphism?

Answer 10

Any variation in the human genome that does not cause a disease on its own but can predispose to a common disease.

Question 11

What is synonymous polymorphism?

Answer 11

Changes in DNA sequence that doesn’t change the amino acid or subsequent protien

Question 12

What is non-synonymous missense polymorphism?

Answer 12

Changes in the DNA and amino acid and protein produced

Question 13

What is non-synonymous nonsense polymorphism?

Answer 13

Changes to DNA to code for a premature stop codon.

Question 14

What are some of the limitations of family studies?

Answer 14

It does not take into account the risk caused by shared environment.

Question 15

How will the liability curve appear for affected relatives?

Answer 15

It will shift to the tight as the familial incidence is higher than the general population

Question 16

Describe why 1st degree relatives of an affected person who in the lower risk group are more likely to get the disease?

Answer 16

For the person in the lower risk group to be affected they would have to have had a greater number of risk factors therefore their relatives are more likely to also have a greater number of risk factors.

Question 17

What are some of the limitations of twin studies?

Answer 17

It doesn’t take into account that being a monozygotic twin can be a predisposing factor for a disease

Question 18

What are the ways of working out if a disease phenotype has genetic contribution?

Answer 18

By recurrence risk in siblings and twin studies

Question 19

What are some of the limitations of association studies?

Answer 19

Difficult if you don’t know what gene or polymorphism to look at and association could be due to chance or to population stratification.

Question 20

How can you find out if a polymorphism contributes to a disease?

Answer 20

Via association study methods - looks at the affected individuals and what polymorphism is increased. Or test the whole genome - Analyse the polymorphisms in a disease and control population.

Question 21

When can you suspect a single gene disorder

Answer 21

If you see a really severe version of a disease that is usually multifactorial

Question 22

For multifactorial conditions there is a higher recurrence risk if?

Answer 22

There are more affected family members and more severely affected family members.