Module 8 - Gene probes, genetic fingerprinting and medical diagnosis

Question 1

What are DNA probes used for?

Answer 1

They are used to locate specific alleles of genes to see if a person’s DNA contains a mutated allele that causes a genetic disorder

Question 2

What are DNA probes?

Answer 2

They are short strands of DNA. They have a specific base sequences that is complementary to a target allele

Question 3

How does hybridisation work?

Answer 3

A sample of DNA is digested into fragments using restriction endonuclease and is separated used electrophoresis. The separated DNA fragments are then transferred to a nylon membrane and incubated with the fluorescently labelled DNA probe. If the allele is present, the DNA probe would have bound to the target DNA and fluorescents. A band will appear

Question 4

What is a DNA microarray?

Answer 4

This is a glass slide with microscopic spots of different DNA probes attached to it in rows.

Question 5

How does a microarray work?

Answer 5

A sample of fluorescently labelled human DNA is washed over the array. If the labelled human DNA contains any sequences which match the probes, it will stick to the array. The array is then washed to remove any labelled DNA that hasn’t stuck. They array is then visualised under a UV light and any spots that appear contain the specific allele

Question 6

What are 3 main uses of DNA probes?

Answer 6

• Identifying inherited diseases
• Determining how a patient responds to drugs
• Helping to identify any health risks

Question 7

What is genetic counselling?

Answer 7

Advising patients and their relatives about the risks of genetic disorders

Question 8

What does screening help a person to identify?

Answer 8

• If they are a carrier to a mutated allele, the type of mutated allele they are carrying and the most effective treatment

Question 9

If someone’s screening is positive, what does genetic counsellors do?

Answer 9

They advise patients on the options of prevention or the treatment available

Question 10

What is personalised medicine?

Answer 10

They are specifically tailored to a person’s DNA. If doctors have you genetic information, they can use it to predict different drugs and only prescribe the ones that will be most effective for you

Question 11

What are VNTR’s?

Answer 11

Base sequences that don’t code for proteins but repeat over and over

Question 12

What is genetic fingerprinting?

Answer 12

Comparing VNTRs between different individuals to determine the relationships or variability

Question 13

Why is the chances of someone having the same VNTRs very low?

Answer 13

It is low because the chancesof someone’s VNTRs containing the same number of repeats and in the same place in the DNA is very low

Question 14

Why is the chances of someone having the same VNTRs very low?

Answer 14

It is low because the chances of someone’s VNTRs containing the same number of repeats and in the same place in the DNA is very low

Question 15

What is electrophoresis?

Answer 15

This is the separation of DNA fragments to produce a genetic fingerprint that can be compared with other individuals

Question 16

Why is a PCR used in electrophoresis?

Answer 16

A PCR is used to make copies of the area of DNA that contains the VNTRs

Question 17

How does electrophoresis work in simple terms?

Answer 17

1. A sample of DNA is obtained
2. A PCR is then used to make copies
3. You will end up with DNA fragments where the length corresponds to the number of repeats the person has at each specific position
4. A fluorescent tag is added to all the DNA fragments so that they can be viewed under a UV light

Question 18

Explain how electrophoresis is set up to prepare a genetic fingerprint?

Answer 18

A DNA mixture is placed into a well in a slab of gel and covered in a buffer solution that conducts electricity. An electrical current is passed through the gel.

Question 19

How does electrophoresis work after they have set it up?

Answer 19

As DNA fragments are negatively charged, they move towards the positive electrode at the far end of the gel. DNA fragments separate according to size with the smallest ones move the fastest and travel the furthest. They are then transferred to a nylon sheet using a sponge. DNA fragments are viewed as bands under a UV light

Question 20

What are the two main reasons as to what genetic fingerprinting is used for?

Answer 20

Determining genetic relationships and determining genetic variability

Question 21

What is meant by determine genetic relationships using genetic fingerprinting?

Answer 21

We develop VNTRs from our parents with half from each of our parents. The more bands that match, the more closely related that they are

Question 22

What is meant by determining genetic variability using genetic fingerprinting?

Answer 22

The more number of bands that don’t match, the more genetic variation between them both. Comparing the number of repeats at several places in the genome for a population to find out how is is genetically varied

Question 23

What is the use of genetic fingerprinting in forensic science?

Answer 23

Comparing samples of DNA collected from crime scenes to samples of DNA from possible suspects

Question 24

How is genetic fingerprinting used in medical diagnosis?

Answer 24

A genetic fingerprint could refer to a unique pattern of several alleles. It can be used to diagnose genetic disorders and cancer.
It is useful when a specific mutation isn’t known or where several mutations could have caused the disorder

Question 25

How can genetic fingerprinting be used in animal and plant breeding?

Answer 25

It can be used to help prevent interbreeding. This is useful because interbreeding can increase the chances of genetic disorders occurring. It could also help identify how closely related individuals are

Question 26

How can DNA be screened for all known harmful mutations in both genes?

Answer 26

• Use of a PCR to amplify DNA fragments
• Cut DNA using restriction endonucleases
• Separate the DNA fragments using electrophoresis
• Add labelled DNA probes which bind to the DNA
• Use of radioactivity or fluorescent to determine any mutations