DNA profiling

Question 1

STEP 1 - How would you extract the DNA?

Answer 1

• The DNA is extracted from cells, tissues, blood
• The DNA is purified
• tiny amounts are needed because the lab techniques can copy the DNA as many times

Question 2

Why does the DNA need to be purified?

Answer 2

• To remove any impurities

Question 3

STEP 2 - How would you digest the same with enzymes?

Answer 3

• DNA sample is cut into smaller fragments using RESTRICTION ENZYME
• They cut both stands and specific enzymes can be chose to cut the DNA at the start of a particular VNTR’s or STR’s that we are looking for.
• This results in different lengths of fragments

Question 4

STEP 3 - How would you separate the DNA fragments?

Answer 4

• GEL ELECTROPHORESIS
• DNA fragments are put into a well block of gel, along with loading dye to make them visible
• placed into alkaline buffer solution which regulated PH and helps carry electrical charge across the gel
• DNA fragments move towards the positive end (the phosphate groups in the DNA give it a negative charge)
• smaller fragments move the furthest

Question 5

Why do the fragments need to be separated?

Answer 5

• the fragments need to be separated in order to look for patterns to be analysed

Question 6

Why is loading gel needed?

Answer 6

• to make the DNA fragments visible

Question 7

STEP 4 - What is hybdrisation?

Answer 7

• DNA probes are added to look for a particular mini/micro - satellites in the DNA
• the probes have complementary base sequence to look for the sequence you are looking for.
• They are 100 - 1000 nucleotides long

Question 8

How would you see the evidence/ make it visible?

Answer 8

• If the probes are used a radioactive or fluorescent then they can be detected wherever they have attached
• Radioactive probes - placing nylon membranes on a x-ray film causes the film to fog
• fluorecent - place the nylon membrane under the uv light and the probes will glow

Question 9

What happens if you place the probes on a fluorescent dye?

Answer 9

• place the nylon membrane under the uv light and the probes will glow

Question 10

What happens if you place the probes on a x -ray film?

Answer 10

• placing nylon membranes on a x-ray film causes the film to fog