8B - Genetic fingerprinting

Question 1

What is genetic fingerprinting?

Answer 1

A technique used by scientists which is based on the fact that the genome of most eukaryotes contains repetitive non-coding pieces of DNA.

Question 2

What are DNA bases which are non-coding and repeating known as?

Answer 2

Variable number tandem repeats (VNTRs)

Question 3

What does VNTR stand for?

Answer 3

Variable number tandem repeats

Question 4

What are variable number tandem repeats?

Answer 4

DNA bases which are non-coding and repeating

Question 5

What is the length of VNTRs like between people?

Answer 5

Different.

Question 6

What are the VNTRs like of people who are closely related?

Answer 6

More similar.

Question 7

What are the stages of genetic fingerprinting?

Answer 7

Extraction
Digestion
Separation
Hybridisation
Development

Question 8

Explain the step of extraction in genetic fingerprinting

Answer 8

DNA extracted from sample (blood, hair, semen, skin).

PCR used to amplify sample if it is small.

Question 9

Explain the step of digestion in genetic fingerprinting

Answer 9

DNA cut into millions of small fragments using restriction endonucleases chosen for their ability to cut close to but not within the core sequences.

The sections of DNA that are cut out are called restriction fragments.

This yields 1000s of restriction fragments of all different sizes as the base sequences being cut may be far apart (long fragment) or close together (short fragment).

Question 10

Explain the step of separation in genetic fingerprinting

Answer 10

Fragments separated on basis of size using gel electrophoresis. DNA fragments are injected into wells and an electric current is applied along the gel. DNA is negatively charged so it is attracted to the positive end of the gel.

Smaller the fragment = faster it moves.

Gel is immersed in alkali in order to separate double strands into single strands. The pattern of fragments are transferred to a nylon membrane by southern blotting.

Southern blotting - Thin nylon membrane laid over gel. The membrane is covered with several sheets of absorbent paper, which draw up the liquid containing the DNA by capillary action. This transfers DNA fragments to the nylon membrane in precisely the same relative positions they occupied on the gel. The DNA fragments are then fixed to the membrane using UV light.

Question 11

Explain the step of hybridisation in genetic fingerprinting

Answer 11

Radioactive (or fluorescent) probes are used to attach to the core sequences.

The probes have base sequences complementary to the core sequence and bind under specific conditions (temp and pH).

Any probes not bound are washed off.

repeated with different probes which bind to different sequences.

Question 12

Explain the step of development in genetic fingerprinting

Answer 12

Nylon sheet place under X-ray film.

The radioactive probes on the DNA fragments expose the film.

This produces visible pattern of light and dark bands which is unique to each individual (except identical twins).

The pattern of fragment distribution is then analysed.

Question 13

Explain how electrophoresis separates DNA fragments to make a genetic fingerprint

Answer 13

1) A sample of DNA is obtained.
2) PCR makes many copies of the areas of DNA containing the VNTRs - primers used that bind to either side of repeated so whole repeat is amplified.
3) End up with DNA fragments where the length (in nucleotides) responds to the number of repeats the person has at each specific position.
4) Fluorescent tag added to all DNA fragments so they can be viewed under UV light.
5) The DNA fragments undergo electrophoresis.
6) The DNA fragments are viewed as bands under UV light - this is the genetic fingerprint.
7) 2 genetic fingerprints can be compared to find a math (same gel location and therefore VNTRs).

Question 14

Explain the process of gel electrophoresis

Answer 14

• DNA mixture 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. DNA fragments are negatively charged, so they move towards the positive electrode at the far end of the gel.
• Small DNA fragments move faster and travel further through the gel, so the DNA fragments separate according to size.

Question 15

What is genetic fingerprinting used to determine?

Answer 15

Determining genetic relationships

Determining genetic variability within a population

Question 16

How can genetic fingerprinting be used to determine genetic relationships?

Answer 16

We inherit VNTR base sequences from our parents. Roughly half of the sequences come from each parent. This means the more bands on a genetic fingerprint that match, the more closely related (genetically similar) two people are.

Question 17

Describe how paternity tests are an example of genetic fingerprinting

Answer 17

Paternity tests are used to determine the biological father of a child be comparing genetic fingerprints. If lots of bands on the fingerprint match, then that person is most probably the child’s father. The higher the number of places in the genome compared, the more accurate the test result.

Question 18

How can genetic fingerprinting be used to determine genetic variability within a population?

Answer 18

The greater the number of bands that don’t match on a genetic fingerprint, the more genetically different people are. This means you can compare the number of repeats at several places in the genome for a population to find out how genetically varied that population is.

E.g. the more the number of repeats varies at several places, the greater the genetic variability within a population.

Question 19

What can genetic fingerprinting be used in?

Answer 19

Forensic science
Medical diagnosis
Animal and Plant breeding

Question 20

Explain how genetic fingerprinting can be used in forensic science

Answer 20

1) DNA isolated from all the collected samples (from the crime scene and from the suspects).
2) Each sample is replicated using PCR (DNA is amplified so enough is produced for it to be seen on the gel).
3) The PCR products are run on an electrophoresis gel and the genetic fingerprints produced are compared to see if any match.
4) If the sample match, it links a person to the crime scene.

Question 21

What samples can be taken from a crime scene?

Answer 21

DNA from blood, semen, skin cells, saliva, hair, etc.

Question 22

Explain how genetic fingerprinting can be used in medical diagnosis

Answer 22

A genetic fingerprint can refer to a unique pattern of several alleles.

It can be used to diagnose genetic disorders and cancer. It’s useful when the specific mutation isn’t known or where several mutations could have caused the disorder, because it identifies a broader, altered genetic pattern.

Question 23

Give examples of how genetic fingerprinting can be used in medical diagnosis

Answer 23

EXAMPLE 1:
Preimplantation genetic haplotyping (PGH) screens embryos created by IVF for genetic disorders before they’re implanted into the uterus. The faulty regions of the parents’ DNA are used to produce genetic fingerprints, which are compared to the genetic fingerprint of the embryo. If the fingerprints match, the embryo has inherited the disorder. It can be used to screen for cystic fibrosis, Huntington’s disease, etc.

EXAMPLE 2:
Genetic fingerprinting can be used to diagnose sarcomas (type of tumour). Conventional methods of identifying a tumour (e.g. biopsies) only show the physical differences between tumours. Now the genetic fingerprint of a known sarcoma (e.g. the different mutated alleles) can be compared to the genetic fingerprint of a patient’s tumour. If there’s a match, the sarcoma can be specifically diagnosed and the treatment can be targeted to that specific type.

Question 24

Explain how genetic fingerprinting be used in animal and plant breeding

Answer 24

Can be used to prevent interbreeding which decreases the gene pool. Interbreeding can lead to an increased risk of genetic disorders, leading to health, productivity and reproductive problems.

Can be used to identify how closely-related individuals are - the more closely-related two individuals are, the more similar their genetic fingerprint will be (e.g. more bands will match). The least related individuals will be bred together.