Genetic Fingerprinting

Question 1

gel electrophoresis

Answer 1

technique used to separate dna fragments according to their size

• dna is extracted from patient’s cell
• add restriction enzyme to digest DNA into fragments
• uses a slab of gel
• electrode placed at each end of the gel + electric current passed through
• sample containing DNA is placed in well
• DNA is neg charged and will move towards positive electrode
• small fragments of dna (vntrs) will move through gel faster than larger

Question 2

VNTR

Answer 2

variable number tandem repeats
DNA has non coding regions
introns- contain variable number tandem repeats
VNTRs are short sequences of dna that are repeated a variable number of times
can be used to identify sources of dna

Question 3

restriction endonuclease

Answer 3

hydrolyse bonds within the dna molecule
break bonds in sugar phosphate backbone
produce sticky ends
cut dna at specific recognition sequences (palindromic)
enzyme has specific active site which is complementary to a sequence before VNTR and allows whole VNTR to be extracted

Question 4

genetic fingerprinting

Answer 4

extraction, digestion, separation, hybridisation, development
EDSHD
every day should have d

Question 5

extraction

Answer 5

sample of dna is extracted from patient’s cell

amplified using PCR to make lots of copies

Question 6

digestion

Answer 6

dna is cut using restriction enzymes

cut close, before and after, the VNTRs

Question 7

separation

Answer 7

fragments of dna are separated by size using gel electrophoresis (same as above)
alkali is added to separate double strands
dna fragments are transferred onto a nylon membrane

Question 8

hybridisation

Answer 8

dna probes are added so you can see the dna
will have fluorescent or radioactive label
bind to specific VNTRs as they have comp bases
different probes bind to different bases

Question 9

development + comparison

Answer 9

nylon sheet can be exposed
if radioactive label was used, X ray will be used
fluorescent can be identified visually
position of dna bands is compared using a marker of known lengths of VNTRs
position of bands is unique to every individual

Question 10

uses

Answer 10

forensic science- genetic fingerprints made form DNA left at the scene of a crime + can be compared to GF of suspects

paternity tests- half of genetic info is inherited from father
each band on a dna fingerprint would have a corresponding band to either mother or father GF

plant + animal breeding- used to prevent undesirable breeding in zoos eg between related individuals

medical diagnosis- eg in huntington’s where a certain base sequences are repeated over and over
>50 repeats means the onset of disease will occur earlier
can compare with: GF of sufferers and of people without disease