Genetic fingerprinting

Question 1

What is genetic fingerprinting?

Answer 1

• A diagnostic tool used in forensic and medical diagnosis
• relies on the genome of DNA contains repetitive, non coding bases of DNA

Question 2

What are VNTRS?

Answer 2

• Variable number tandem repeats are non coding DNA bases
• For every individual the number and length of VNTRs has an unique pattern
• They are different in all individuals except identical twins and the probability of two individuals have the same sequence of VNTRs is very small
• The more closely related individuals are, the more similar the VNTRs will be

Question 3

What is gel electrophroesis?

Answer 3

• it is used to seperate DNA fragments according to their size
• DNA fragments are placed on to an agar gel and a voltage is applied to it
• The resistance of the gel means that the larger the fragments, the slowly they move
• Therefore, over a fixed period of time the smaller fragments move further than the larger ones
• If the DNA fragments are labelled, their final positions in the gel can be determined by placing a sheet of X ray film over the gel
• only DNA fragments up to 500 bases can be sequenced and larger genes need to be cut into smaller fragments by restriction endonucleases

Question 4

What are the steps of making a genetic fingerprint?

Answer 4

• extraction
• digestion
• seperation
• hybridisation
• development

Question 5

What occurs during extraction?

Answer 5

• Extract the DNA by seperating it from the rest of the cell
• As the amount of DNA is small, its quantity can be increased using the polymerase chain reaction

Question 6

What happens during digestion?

Answer 6

• The DNA is then cut into fragments using the same restriction endonucleases
• The endonucleases are chosen for their ability to cut close to the target DNA

Question 7

What happens during seperation?

Answer 7

• The fragments of DNA are then seperated according to their size by gel electrophoresis under the influence of an electrical voltage
• the gel is then immersed in alkali in order to seperate the double strands into single strands

Question 8

What occurs during hybridisation?

Answer 8

• Radioactive DNA probes are now used to bind with VNTRs
• The probes have base sequences which are complementrary to the base sequences of the VNTRs and bind to them under specific conditions such as temperature and pH
• This is carried out with different probes which bind to different target DNA sequences

Question 9

What happens during development?

Answer 9

• X ray is put over the nylon membrane
• The film is exposed by radiation from radioactive probes
• The points correspond to the position of the DNA fragments as seperated during electrophoresis, a series of bars is revealed
• The pattern of bands is unique to every individuals except identical twins