Genetic Screening & Counselling

Question 1

What are DNA probes?

Answer 1

short, single-stranded pieces of DNA that are labelled radioactively or fluorescently so that they can be identified

Question 2

What are DNA probes used for?

Answer 2

They are used to locate specific alleles of genes

Question 3

What does the use of DNA probes allow us to do?

Answer 3

To screen patients for heritable conditions, drug responses or health risks

Question 4

How are DNA created, what particular feature do they have?

Answer 4

DNA probes are created to have a complementary base sequence to the allele that is being screened for

Question 5

How do they go about mixing the DNA probe with the patient’s DNA?

Answer 5

The patient’s DNA sample is treated to make it single-stranded and then it is mixed with the DNA probes

Question 6

What does hybridisation mean?

Answer 6

It is when the DNA probe will ‘hybridise’ if the patient has that particular allele - the label indicates its presence.

Question 7

Define the term hybridise:

Answer 7

join together, in this case, the DNA probe and the patient’s single stranded DNA

Question 8

Name the two processes that make up DNA hybridisation:

Answer 8

Denaturation and Annealing

Question 9

Describe the process denaturation during DNA hybridisation:

Answer 9

The patient’s DNA sample is heated to make it single-stranded
The heat causes the hydrogen bonds between bases to break

Question 10

Describe the process of annealing during DNA hybridisation:

Answer 10

The patient’s single stranded DNA sample is mixed with the DNA probe and cooled so that any complementary sequences that have aligned, can form hydrogen bonds between the bases.

Question 11

What else could anneal apart from the DNA probe to the patient’s DNA?

Answer 11

Some of the patient’s DNA samples will anneal back together, but some will anneal with the DNA probe

Question 12

Give an example of a DNA sequencing technique:

Answer 12

The Sanger method

Question 13

In order to locate a specific allele, what must be known?

Answer 13

The DNA base sequence must be known to then create the DNA probe

Question 14

How can we find out the DNA base sequence of the specific allele in order to create the DNA probe?

Answer 14

It can be determined using DNA sequencing techniques

Question 15

How can we produce a DNA fragment for the DNA probe?

Answer 15

gene machine

Question 16

How do we amplify the DNA fragment in order to make multiple DNA probes?

Answer 16

Using the polymerase chain reaction (PCR)

Question 17

What happens to the DNA probe after it has been amplified using PCR?

Answer 17

The label is then added

Question 18

What are the two possible labels that you can add to the DNA probe?

Answer 18

A radioactive nucleotide which contains the isotope (32)P
OR
A fluorescent label which emits light under UV light

Question 19

What is the next step after DNA hybridisation?

Answer 19

The DNA is washed so that any unbound DNA probes are washed away

Question 20

What indicates whether the allele of interest is present in the patient’s DNA?

Answer 20

The presence of the radioactive or the fluoresence label

Question 21

Describe what happens during genetic screening and what apparatus is used?

Answer 21

A microarray is used which has multiple DNA probes on it all with complementary sequences to a range of specific alleles.

Question 22

What can genetic screening be used for?

Answer 22

This method can be used to screen for potential genetic disorders or for ‘cancer-causing oncogenes’

Question 23

How is a micro-array more efficient?

Answer 23

It can be used to screen for multiple diseases simultaneously where multiple different DNA probes are attached

Question 24

Why might someone want to have their DNA screened?

Answer 24

Personalised medicine, so the drug that you take can be tailored for your paticular genotype

Question 25

What are the advantages of genetic screening enabling personalied medicine?

Answer 25

Certain drugs, painkiller, can become more/less effective depending on your genotype.
It can help determine the best dose, which increases the effectiveness, safety + saves money

Question 26

Give an example representing why having your DNA screened is important:

Answer 26

Some diabetics with a particular genotype can take vit.E to reduce their chances of developing cardiovascular disease whereas for other diabetics with a different genotype, it will increase their chances.

Question 27

What is genetic counselling?

Answer 27

It is like a type of social work, where people can have their family history researched to consider the likelihood of them carrying any alleles linked to diseases before starting a family, or for their general health.

Question 28

During genetic counselling, what are patients informed of?

Answer 28

Any potential risks to themselves or to their future offspring if they were to carry the allele.

Question 29

What are some disorders that people can screen for?

Answer 29

Sickle-cell anaemia, cystic fibrosis, and if there is a family history of breast cancer: you could then opt for a masectomy or regular screening for tumours and reduce environmental risk factors.