Genetic Diseases

Question 1

Give three broad causes of disease.

Answer 1

Genetic e.g. Cystic fibrosis
Environmental - main cause of death in third world countries e.g. infection
Multifactorial - main cause of disease in developed countries e.g. diabetes

Question 2

What term is given to the position of a gene?

Answer 2

Locus

Question 3

Which chromosomes are autosomal?

Answer 3

1-22.

Question 4

What is a genotype?

Answer 4

Genetic constitution of a person.

Question 5

What is a phenotype?

Answer 5

Appearance of an individual as a result of their genotype.

Question 6

What is the term given to alternative forms of a gene at a specific locus?

Answer 6

Allele

Question 7

What is a normal allele called?

Answer 7

Wild type

Question 8

What is polymorphism?

Answer 8

Frequent hereditary variations at a locus. Can make you more or less susceptible to a disease.

Question 9

What is the term given to two relatives who reproduce?

Answer 9

Consanguinity

Question 10

What does homozygous mean?

Answer 10

Both alleles are at the same locus

Question 11

What does heterozygous mean?

Answer 11

Alleles at a locus are different.

Question 12

Which term refers to genes being carried on an unpaired chromosome - i.e. a locus on an X chromosome in a male?

Answer 12

Hemizygous

Question 13

What does penetrance mean?

Answer 13

Proportion of people with a gene who show the expected phenotype

Question 14

Which term is given to the fact that there is variation in clinical features between patients of a genetic disorder?

Answer 14

Variable expression

Question 15

If a multifactorial condition is more common in males, which relatives (in terms of sex) will have a higher risk?

Answer 15

The female relatives

Question 16

What does congential mean?

Answer 16

Condition manifested at birth

Question 17

Which pattern of inheritance results in disease only manifesting if in the heterozygous state?

Answer 17

Autosomal dominant. One defective gene required.

Question 18

What is the only pattern of inheritance that allows disease to be passed from male to male?

Answer 18

Autosomal dominant

Question 19

When would parents be unaffected by an autosomal dominant disease?

Answer 19

1. Don’t have genes for it
2. Gonadal mosaicism
3. Mother has reduce penetrance or variable expression

Question 20

What is autosomal recessive inheritance?

Answer 20

A disease that manifests in the homozygous state. Two defective genes required.

Question 21

What % chance will the offspring have the condition and be a carrier if the parents are carriers?

Answer 21

25% chance offspring having condition

2/3 chance offspring will be a carrier

Question 22

What is the most common autosomal recessive condition affecting whites in the UK?

Answer 22

Cystic fibrosis. Incidence = 1 in 25,000

Question 23

Who should you disregard when calculating risk of carriers in offspring?

Answer 23

The already affected child. If one child is unaffected, one is affected and 2 are carriers, then the chance of being a carrier is 2/3 NOT 1/2.

Question 24

What causes X-linked inheritance?

Answer 24

A mutation in genes on the X chromosome.

Question 25

Why is there no male-to-male transmission of X linked inheritance?

Answer 25

Sons always get their x chromosome from the mother.

Question 26

Which sex is more likely to be affected by X-linked disease?

Answer 26

Males. Males can never be carriers, they are usually affected. Females are usually unaffected.

Question 27

What is lyonisation?

Answer 27

The process of X chromosome inactivation. One of two X chromosomes in every cell in a female is randomly inactivated early in embryonic development.

Question 28

Why does lyonisation occur?

Answer 28

To prevent female cells having twice as many gene products from the X chromosome as males.

Question 29

Describe Knudson’s 2-hit hypothesis.

Answer 29

Gene mutations may be either inherited or acquired.

Question 30

According to Knudson’s 2-hit hypothesis, how are hereditary cancers formed?

Answer 30

1 inherited mutation + 1 acquired mutation

Question 31

According to Knudson’s 2-hit hypothesis, how are sporadic cancers formed?

Answer 31

2 acquired mutations

Question 32

Which parent is mitochondria inherited from?

Answer 32

Mother. Men cannot pass on mitochondrial mutations.