Genetic diseases

Question 1

What is a genotype?

Answer 1

The genetic composition of an individual

Question 2

What is a phenotype?

Answer 2

Appearance of an individual that results from the interaction between the environment and the genotype

Question 3

What’s a karyotype?

Answer 3

Number and visual appearance of the chromosomes in the cell nuclei

Question 4

What is meant by an autosomal dominant condition?

Answer 4

Affects autosomal chromosomes (1-22)

Dominant - manifests in heterozygous state

50% chance of child developing disorder is 1 parent is affected

Question 5

What is meant by an autosomal recessive condition?

Answer 5

Affects autosomal chromosomes (1-22)

Recessive - manifests in homozygous state - two affected alleles

Incidence of carriers

Question 6

What is a good way to recognise a condition is autosomal and not sex/linked?

Answer 6

Male to male transmission

NOT SURE IF THIS IS RIGHT

Question 7

What’s an allele?

Answer 7

One or more alternatives of a gene at a given location (locus)
For example:
Gene: eye colour gene
Allele: Blue eye colour

Question 8

In autosomal recessive and dominant conditions, are males and females affected equally?

Answer 8

Yarp

Question 9

In what circumstances can autosomal recessive conditions be passed on? What’s the probability of having an affected child?

Answer 9

When both parents are carriers of a defective allele

1/4 chance child has disease

Question 10

What is an X-linked condition?

Answer 10

A disease that occurs due to a defective allele of a gene carried on the X chromosome

Question 11

How are males an females affected differently by X-linked diseases?

Answer 11

Males get the disease, as they only have one X chromosome, there isn’t another one to back it up!

Females are carriers of the disease as they have another X chromosome that is likely to be healthy

Question 12

Give an example of a disease which is: A. dominant, A. recessive, X-linked

Answer 12

A. dominant - Huntington’s
A. recessive - Cystic Fibrosis
X-linked - Haemophilia

Question 13

Look at some pedigrees!

Answer 13

Or else.

Question 14

Explain Knudson’s 2 hit hypothesis.

Answer 14

A cell can only initiate a tumour when it contains 2 mutant alleles

A person who inherits a mutant allele must experience a second somatic mutation for a tumour to start developing

Question 15

What is meant by lyonisation?

Answer 15

When one of the X chromosomes in each cell of a female is inactivated

Normal process that has to happen to prevent females having twice as many gene products as males

Remember the tortoiseshell cat! Mosaic

Question 16

What is gonadal mosaicism?

Answer 16

When germ cells are a mixture of 2 or more genetically different cell lines

For example: half a man’s sperm cells are healthy and half have an abnormality

Question 17

How does gonadal mosaicism affect offspring?

Answer 17

The father will be healthy as the mutation likely occurred after birth and only affects his sperm

Genetic abnormality can affect some or all of the children

Question 18

What is meant by penetrance?

Answer 18

The percentage of people with the mutation that causes the disease that actually have a defective phenotype (show symptoms)

Question 19

What is meant by variable expression?

Answer 19

Different people with the same genetic mutation showing a range of signs/symptoms - mild or severe form of the disease

Question 20

What are multifactorial conditions?

Answer 20

Diseases that are due to a combo of genetic and environmental factors

Most of the common diseases are multifactorial

Question 21

What is meant by the dominant negative effect?

Answer 21

A dominant allele that has a negative effect on the function the allele should perform
Or something along those lines!

Question 22

What’s the difference between Mendelian and multifactorial inheritance?

Answer 22

Mendelian - diseases inherited by a single gene

Multifactorial - a result of interplay between genetic and environmental factors